This anecdote is found among notes for additions to a manuscript memoir of the composer and music theorist Anton Reicha (1770–1836). The memoir and notes survive in two copies; neither is in Reicha’s own hand, but their content is held to be genuine. For the anecdote given here, the textual differences between the two copies are inconsequential (for details, see the discussion in the Notes below).

Reicha was raised by his uncle Joseph, and the two came to Bonn in 1785, when Joseph took up the position of concertmaster in the court orchestra of the Elector of Cologne. Anton was 15 years old at the time, just 10 months older than Beethoven, and the two teenagers soon became friends. Anton joined the court orchestra by 1790, when his name first appears in the court calendar; he is listed there both as a violinist and as second flute. The same calendar shows Joseph Reicha as director of the orchestra, Ludwig van Beethoven as organist and violist, Beethoven’s sometime teacher Christian Gottlob Neefe as organist and violinist, and the music dealer and publisher Nikolaus Simrock as first horn (on Neefe as Beethoven’s teacher, see May 1999).

Anton Reicha’s anecdote tells of hearing an unnamed countess sing scene 6 in D minor from Mozart’s Idomeneo. The performance had such an impact on young Anton and his friend Beethoven that they could think of little else for days, and Anton vividly recalled the performance decades later. The scene is Elettra’s “Tutte nel cor vi sento” and its preceding accompanied recitative; the singer was almost certainly Countess Maria Anna Hortensia von Hatzfeld, Mozart’s Elettra in the production of Idomeneo at the theater of Prince Auersperg in Vienna in Mar 1786 (see our entry on that production). Countess Hatzfeld is said to have lived in Vienna in her youth, but by the 1780s she was based in Bonn, where her husband Count Clemens August Johann Nepomuk von Hatzfeld (1743–1794) was an official in the electoral court.

The viola-playing Elector in Reicha’s anecdote is Maximilian Franz (1756–1801), the youngest brother of Emperor Joseph II; Max Franz became Elector of Cologne in 1784 following the death of his predecessor Count Maximilian Friedrich von Königsegg-Rothenfels (1708–1784; on Max Franz as violist, see Magazin der Musik, ii:959).

Reicha gives no hint of the date of Countess Hatzfeld’s performance of “Tutte nel cor vi sento,” and little is known about concerts at court in Bonn during this period. However, the performance must have taken place at some point between 1785, when Reicha arrived in Bonn, and Nov 1792, when Beethoven left permanently for Vienna. But it seems unlikely that “Tutte nel cor vi sento” would have had quite such a profound impact on young Reicha and Beethoven if they had already heard the even more astonishing Don Giovanni, first performed in Bonn on 13 Oct 1789 (see our entry on that performance); so we may tentatively suggest that the Countess’s performance took place before that date. It might be thought that her performance in Bonn likely followed her appearance as Elettra in Auersperg’s production of Idomeneo in Vienna in Mar 1786. But Robert Münster has shown that a member of the Hatzfeld family (quite possibly Count Franz Ludwig von Hatzfeld, one of the Countess’s brothers-in-law) owned scores of Elettra’s arias as early as 1783 (Münster 2001, 92–94); given the direct family connection, we cannot rule out the possibility that Countess Hatzfeld had already known and performed “Tutte nel cor vi sento” before Auersperg’s production. From a cautious perspective, then, we can suggest that the Countess’s performance in Bonn took place somewhere in the years 1785 to 1789. To understand the impact on young Reicha and Beethoven, we have to imagine what it would have been like to hear “Tutte nel cor vi sento” for the first time, before knowing Don Giovanni and before Beethoven had written the works of Beethoven.

Countess Maria Anna Hortensia von Hatzfeld was born Countess Zierotin in 1750. The exact date of her birth appears to be unknown, as is the place, but the Zierotins were an old Moravian aristocratic family with a seat in Bludov. Little is known about the Countess’s early years, although Neefe, in a long report on music in Bonn in 1783, writes that she “ist von den besten Meistern im Singen und Clavierspielen zu Wien unterrichtet worden” (“[she] was instructed in singing and keyboard playing by the best masters in Vienna”; Magazin der Musik, i:387). Maria Anna Hortensia von Zierotin and her sister Franziska (1745–1831) were grandnieces of Elector Maximilian Friedrich von Königsegg-Rothenfels; their mother, Countess Maria Josepha von Zierotin, née Countess von Königsegg-Rothenfels (1724–1785), was the oldest daughter of Max Friedrich’s older brother Carl Ferdinand (for the Zierotin sisters, see this modern genealogy; for the Königsegg-Rothenfels line, see this genealogy from 1771). We do not know precisely when the sisters moved to Bonn, but in 1767 Franziska married Maximilian Karl Heinrich Joseph von Taxis, who apparently resided in Cologne, and in 1775 Maria Anna Hortensia married Count Clemens August Johann Nepomuk von Hatzfeld.

Genealogies published during Countess Hatzfeld’s lifetime (and subsequent scholarship based on them) give the date of her marriage as 1772 (see, for example, this genealogy from 1794 and Braubach 1949, 323), but this is incorrect. The marriage took place on 26 Feb 1775 in the Deutschordenskirche, St. Elisabeth, in Vienna.

Through this marriage Countess Hatzfeld became sister-in-law to (among others) her husband’s younger half-brothers August Clemens (1754–1787)—for whom Mozart wrote the solo violin part in the scena con rondò “Non temer, amato bene,” K. 490, for Auersperg’s Idomeneo in 1786—and Hugo Franz (1755–1830), whose 1786 letter regarding Idomeneo we discuss elsewhere on this site. (On August Clemens, see our entry on Auersperg’s Idomeneo; on Hugo, see our entry for 23 Mar 1786.)

On 6 May 1775 the Wienerisches Diarium reported that Countess Hatzfeld had been made a member of the Sternkreuzorden (Order of the Starry Cross) by Empress Maria Theresia:

Bey dieser Gelegenheit geruheten Al=
lerhöchst Ihre Majestät nachfolgenden Da=
men in den hochadelichen Sternkreuzor=
den allergnädigst aufzunehmen:
[...]
Maria Anna Hortensia Gräfinn v. Hatz=
    feld, gebohrne Gräfinn von Zierotin [...]
[WD, no. 30, Sat, 6 May 1775, [6]]

On this occasion, Her Sovereign Majesty
most graciously vouchsafed to accept the
following ladies into the aristocratic
Sternkreuzorden:
[...]
Maria Anna Hortensia, Countess von Hatzfeld,
    née Countess von Zierotin [...]

Countess Hatzfeld’s only known child, a daughter, Maria Theresia (1776–1838) was baptized at the Hofburgpfarre in Vienna on 9 Jan 1776.

Countess Hatzfeld’s own mother, Countess Maria Josepha von Zierotin, died in Vienna on 5 Jun 1785 at no. 759^I in the Untere Bäckerstraße, now Sonnenfelsgasse (WZ, no. 47, Sat, 11 Jun 1785, 1387); the house was part of the Kölner Hof, torn down in 1793.

Countess Hatzfeld’s life has been little studied. At present, apart from Reicha’s anecdote, nothing specific is known about her musical activities in Bonn, and our knowledge of her activities in Vienna, musical and otherwise, is haphazard. Nearly all of her known performances in Vienna are documented solely in the diaries of Count Zinzendorf; the musical references in these diaries have been comprehensively mined only for the period 16 Apr 1783 to 8 Apr 1792 (Link 1998), so there are likely other references to Countess Hatzfeld still to be found before or after those dates.

The following table lists all of Countess Hatzfeld’s known performances in Vienna as a singer or actress (those in 1774 were under her maiden name, Countess Zierotin):

The 17 documented performances in the table place Countess Hatzfeld in Vienna in 1774 and 1778, then each year from 1782 to 1786, and again in 1793; she may, of course, have visited Vienna in other years for which we have no documentation. Seven of the performances in the table are operas, three are plays, and seven are vocal performances at private gatherings. All of the operas and plays were given in private theaters or houses, but there is evidence to suggest that at least some of the performances in Auersperg’s theater may have been open to the public in something like the modern sense (see our entry on Auersperg’s Idomeneo).

Countess Hatzfeld’s documented performances in Vienna tend to be grouped together within relatively short periods of time, a pattern consistent with short visits from Bonn. In 1784, she is known to have appeared four times in five different works within a span of 18 days, all at Prince Liechtenstein’s in Vienna: in two plays on 7 Mar; as Rose in Monsigny’s Rose et Colas on 14 Mar; with Baroness Anna von Pufendorf (Mozart’s Ilia in 1786); in Vincenzo Righini’s Piramo e Tisbe on 21 Mar; and finally as (in Zinzendorf’s words) “la jeune personne” (presumably Agathe) in Grétry’s L’ami de la maison on 25 Mar.

According to Gottron, on 25 Oct 1784 a “Comtesse v. Hatzfeld” sang the role of Rosina in an amateur performance of Paisiello’s Il barbiere di Siviglia at the electoral court in Mainz (Gottron 1959, 164). This may well have been Maria Anna Hortensia, who had many connections to the court in Mainz through her husband’s family (see our entries on Hugo von Hatzfeld’s letter to Großmann and Idomeneo at Prince Auersperg’s).

Countess Hatzfeld was by all accounts a formidable and expressive singer, who sang at a professional level. Schönfeld’s description in the Jahrbuch der Tonkunst von Wien und Prag in 1796 is particularly enlightening:

⁣    Hatzfeld, Gräfinn von; Diese Dame
ist eine besondere Liebhaberinn, Kennerinn
und Beschützerinn der Tonkunst; sie hat ei=
ne der stärksten und klärsten Bruststimmen,
die es giebt; sie hat sehr viel Geläufigkeit
in Passagen, einen herrlichen Triller, und
schöne Manieren, und ist überhaupt ganz
geeignet für den großen erhabenen Gesang
und Bravourarien. In der Kraft erhebt sie
das Herz, in der Oper (beim Privattheater)
erregt sie Bewunderung, und in einem Kon=
zertsaale macht sie Vergnügen. Ihre aus=
übende Kunst übersteigt die gewöhnliche Di=
lettantenfähigkeit in mancher Betrachtung.
[Schönfeld 1796, 25]

⁣    Hatzfeld, Countess von. This lady is
a special amateur, connoisseur, and
protector of music; she has one of the
strongest and clearest chest voices that
exists; she has very great fluency in
passage work, a magnificent trill, and
beautiful embellishments, and is in general 
entirely suited to grand sublime singing
and bravura arias. In her strength she
elevates the heart, in opera (in private
theater) she excites admiration, and in
a concert hall she gives pleasure. Her
practiced art surpasses the usual abilities
of a dilettante in many respects.

Her first documented performance in an opera was the title role in Righini’s Armida on 23 Jul 1782 at the theater of Prince Auersperg. Zinzendorf attended:

[Tue] 23. Juillet. [...]
[...] allois chez le P^ce: adam auersperg [...]

                                                              Le Theatre com
mença a 7h ½ M^e: de Hazfeld armide, M^elle: augenbruk[er]
Renaud. M^r: Aubain Ubaldo. musique de Righini peu saillante.
[les] acteurs jouerent a merveille. moi enfonce dans la loge avec l’ar-
chiduc, Cobenzl, beaucoup de Dames. [...]
[HHStA, Zinzendorf Tagebücher, 1782]

Tue, 23 July. [...]
[...] [I] went to Prince Adam Auersperg’s [...]

                                                              The theater
began at 7:30. Madame de Hatzfeld Armide, Mademoiselle
Auenbrugger Renaud, Monsieur Aubain Ubaldo, music by
Righini unremarkable. The actors played marvelously. I was
squeezed in the box with the Archduke, Cobenzl, and many
ladies. [...]

On 14 Oct 1783, Zinzendorf was at the residence of the Russian ambassador, Prince Galitzin, “ou M^e de hazfeld chanta en imitant la Storace” (“where Madame de Hatzfeld sang imitating Storace”; Link 1998, 213); Nancy Storace had made her debut with the company of the court theater in Vienna just a few months earlier, on 22 Apr 1783. On 14 Mar 1784 Zinzendorf heard Countess Hatzfeld sing the role of Rose “a merveille” (“marvelously”) in Monsigny’s Rose et Colas at Prince Liechtenstein’s (Link 1998, 219), and a week later he found Countess Hatzfeld and Baroness Pufendorf “a ravir” (“ravishing”) in Righini’s Piramo e Tisbe at Liechtenstein’s (Link 1998, 221).

Countess Hatzfeld’s performance of the title role in Gluck’s Alceste in the theater of Prince Auersperg on 12 Feb 1786 made a particularly strong impression:

[...] 12. Fevrier. [...]
                                                              A 5h ½ chez le P^ce:
adam auersperg. [...]

L’opera d’alceste ne commença qu’a 6^h ¾. M^e. d’hazfeld
née Zierotin joua ce role dans la grande perfection, surtout
les airs Non vi turbate, no, [&c], et l’air du cri.

12 February [...]
                                                              At 5:30 pm at Prince
Adam Auersperg’s. [...]

The opera Alceste did not begin until 6:45. Madame de Hatzfeld
née Zierotin played this role with great perfection, above all
the arias “Non vi turbate, no, &c.” and the aria of the cry.

“Non vi turbate, no” is Alceste’s aria at the end of scene 2 of Act II of Gluck’s opera, and the “l’air du cri” may have been Alceste’s “Ah per questo già stanco core” at the end of the Act II. (For a longer extract of this passage and further discussion, see our entry on Auersperg’s Idomeneo.) Four decades later, tenor Michael Kelly also recalled her performance in this role:

⁣                                 I had the honour
of being patronized by Prince Ausberg [sic]. [...]

⁣                 His Highness also was a great
patron of musical performances. He had a beau-
tiful theatre in his palace, at which I saw the
Countess Hatzfeld perform inimitably well, in
Gluck’s serious opera of “Alceste.”—She was a
charming woman, and full of talent.
[Kelly 1826, i:201]

An anonymous writer in the short-lived journal Pfeffer und Salz, after criticizing Mozart’s Idomeneo at Auersperg’s in Mar 1786 as “mit Accompagnement zu sehr überfüllte” (“too overladen with accompaniments”), raved about Countess Hatzfeld’s performance as Elettra:

⁣    Die Gräfin Hatzfeld, welche vor=
treflich singt, und (ohne eben den
Verdiensten der Gräfin Buffendorf die
beym F. Auersberg mitsang, zu nahe zu
treten), unsere Storaze fast übertrift,
hat Hrn. Mozarten ein ansehnliches Ge=
schenk gemacht. Wäre Herr Mozart
reicher als die Gräfin, so wärs hier
an ihm gewesen, Geschenke auszuthei=
len: Denn seine Opera hat durch die
Kunst der Gräfin, nicht sie durch die
Opera in den Augen der Kenner gewon=
nen.
[Pfeffer und Salz, 1786, i:15–16, punctuation corrected]

⁣   The Countess Hatzfeld, who sings
splendidly, and (without wishing to
disparage the merits of Countess [sic]
Pufendorf, who also sang at Prince
Auersperg’s) nearly surpasses our Storace,
has given Herr Mozart a considerable gift.
Were Herr Mozart richer than the Countess,
it would be on him to dispense gifts:
for his opera gained in the eyes of
connoisseurs through her singing,
not she through the opera.

(For a longer extract of this passage and fuller discussion, see our entry on Auersperg’s Idomeneo.)

Countess Hatzfeld’s last documented performance was as Aspasia in Salieri’s Axur in Auersperg’s theater on (probably) 18 Nov 1793. Zinzendorf, who did not attend the performance, remarked in his diary that her performance had been the topic of conversation that evening at the Russian ambassador’s:

18. Novembre. [...]
                                        Dinée chez l’Amb. de Russie [...]

                                                     On parle beaucoup de
l’opera d’Axur, qui se joue au Théatre du P^ce: auersberg
par M^e: de Hazfeld [...]

18 November. [...]
Dined at the Russian ambassador's [...]

                                                    There was much discussion of
the opera Axur, which was played at the theater of Prince
Auersperg by Madame de Hatzfeld.

Her performance in Axur was also singled out in a short report on Auersperg’s theater printed in the Wiener Theater-Almanach für das Jahr 1794:

[...]     Heuer gab der Adel auf demselben
Hrn. Salieri’s beliebte Oper: Axur, auf
welcher die Frau Gräfinn von H** die Rol-
le der Aspasia vortrefflich sang.
[Wiener Theater-Almanach für das Jahr 1794, 58]

⁣         This year [i.e. 1793] the nobility gave in the
same [theater] Herr Salieri’s popular opera
Axur, in which Countess von H[atzfeld]
sang the role of Aspasia splendidly.

The following year, the almanac mentioned her performance again, this time not hiding her identity:

[1]

⁣                      Nachricht
              von Privattheatern.
[...]

[4]

⁣     Das zweyte hervorstehende Privatthea-
ter war im fürstlich Auerspergischen Hause.
Heuer gab diese Gesellschaft zu wiederhol-
ten Mahlen die grosse Oper des Herrn Sa-
lieri, Axur, Rè d’ Ormus. Frau Grä-
finn von Hatzfeld sang und spielte die
Rolle der Aspasia vortrefflich. Auf zwey
Zuschauer machte ihre Darstellung so tie-
fen Eindruck, dass sie ihre Empfindungen
in den zwey folgenden Gedichten äusser-
ten.
[Wiener Theater-Almanach für das Jahr 1795, 4]

⁣                      News
              of Private Theaters
[...]

⁣     The second prominent private theater
was in the house of Prince Auersperg.
This year [1794] the company gave several
repetitions of the great opera by Herr Salieri,
Axur re d’Ormus. Countess von Hatzfeld
sang and played the role of Aspasia splendidly.
Her performance made such an impression
on two in the audience that they expressed
their feelings in the two following poems.

The poems follow, one in French:

and one in Italian:

The reference to Aspasia and Fiametta as mother and daughter (which the characters are not) implies that Countess Hatzfeld’s daughter Maria Theresia sang the role of Fiametta in Auersperg’s production of Axur. She was just 17 years old at the time of Zinzendorf’s diary entry on the production on 18 Nov 1793. We do not know who sang the roles of Axur or Atar.

In his long 1783 report to the Magazin der Musik on musical life in Bonn, Neefe writes that Countess Hatzfeld was a brilliant and expressive pianist as well:

Frau Gräfin von Hatzfeld, ist von den besten
Meistern im Singen und Clavierspielen zu Wien un=
terrichtet worden, denen sie in der That viel Ehre
macht. Das Recitativ declamirt sie vortreflich, auch
parlante Arien hört man von ihr mit Vergnügen. Auf
dem Fortepiano spielt sie sehr brillant, und überläßt
sich dabey völlig ihrem Gefühl. Deswegen hört man
oft das Tempo rubato von ihr, ohne das sie tact=
schwankend ist. Für Tonkunst und Tonkünstler ist sie
enthusiastisch eingenommen.
[Magazin der Musik, i:387–88]

Frau Countess von Hatzfeld was instructed
in singing and keyboard playing by the best
masters in Vienna, to whom she in fact does
much honor. She declaims recitative excellently,
and one hears her with pleasure in parlante arias.
She plays very brilliantly on the fortepiano, and
gives herself over completely to her feelings. For
that reason one often hears tempo rubato from
her, without her having an unsteady beat. She is
enthusiastically smitten by music and musicians.

Two manuscript copies of the so-called vocal “Notturni” attributed to Mozart—K. 346, K. 436–439, and K. 549—bear dedications to Countess Hatzfeld on their title pages; both title pages name Mozart’s friend Gottfried von Jacquin as the composer (on these manuscripts, see Edge 2001, 699–708). The copy in the music collection of the Staatsbibliothek zu Berlin (Mus. ms. 15166) is entirely in the anonymous hand that Edge calls Viennese Mozart-Copyist 1, one of the most important Mozart copyists in Vienna during and just after the composer’s lifetime. The title page of the Berlin copy reads:

Sei Notturni / dedicati / A Sua Eccellenza la Signora / Contessa Hortensia d’Hatzfeld / e composti / [Dal umilissimo Servo Godofredo / nobile de Jacquin]

The original attribution was later covered by a paste-over with the attribution “di / Wolfgango Amadeo Mozart” written in a different hand.

The archive of the Gesellschaft der Musikfreunde in Vienna possesses a similar score of the “Notturni,” likewise mostly in the hand of Viennese Mozart-Copyist 1 (VI 569/Q 3817; K. 549 is in the hand of Maximilian Stadler). The title page of that copy, although now somewhat faded and partially obscured by later overwriting, appears originally to have read identically:

Sei Notturni / dedicati / A Sua Eccellenza la Signora Contessa / Hortensia d’Hatzfeld / e composti / Dal umilissimo [servo] Godofredo / nobile de Jacquin

(Both title pages are reproduced in facsimile in Mörner 1971, xx.)

The thorny question of the attribution and date of the “Notturni” is beyond the scope of this commentary. It suffices here to note that some material for the “Notturni” survives in Mozart’s hand, and it is plausible to think that the pieces may have been collaborations between Mozart and Jacquin. The paper-types of the autograph material suggest a date no earlier than 1787.

The attribution of the aria “Io ti lascia, o cara, addio,” K. 621a, has been perhaps even more contentious (see Edge 2001, 655–63). An autograph leaf of the final 17 measures of the aria survives in the collection of the Mozarteum in Salzburg; in the autograph, the aria is scored for bass voice and strings, and is in the key if E-flat major. However, a manuscript copy of the aria survives in the same library with an attribution to Jacquin (Salzburg, Mozarteum, M. N. 53(a)). This version is scored for soprano, strings, and winds, and is in the key of G major. This copy, like those of the “Notturni,” is in the hand of Viennese Mozart-Copyist 1. The title page reads:

The original attribution has been thoroughly crossed out and replaced by “Mozart” in a different hand. (For a facsimile of this title page, see Edge 2001, 572.) Constanze Mozart believed that Jacquin had composed the melody and that Mozart had added the string parts; she also believed that Jacquin had written the aria for the departure of Countess Hatzfeld (Edge 2001, 656–57). The paper-type of the autograph (Tyson 95) is one that Mozart acquired after his return to Vienna from Prague in Nov 1787 following the premiere of Don Giovanni.

A plausible reading of the evidence is that Jacquin wrote the melody (and perhaps the text) of this short aria for the departure of Countess Hatzfeld—who visited Vienna often, but lived in Bonn—and asked Mozart to orchestrate it. Given that the original version of K. 621a was for bass voice, it seems reasonable to think that Jacquin intended it for himself to sing at some private function attended by Countess Hatzfeld. The later transposition for soprano suggests that this version might have been made for the Countess herself. At present we have no documentary evidence that Countess Hatzfeld was in Vienna in 1787 or 1788, the most likely dates for K. 621a and the “Notturni,” but it would not be at all surprising to discover that she had been. On the evidence of these manuscripts, it seems likely that Jacquin, who was only 20 years old in 1787, had a crush on the Countess.

Countess Hatzfeld’s fine musicianship and her deep interest in music led several prominent composers to dedicate works to her. The most famous is Beethoven’s 24 Variations on Righini’s Arietta “Venni, Amore,” WoO 65, a technically difficult set that speaks highly of the Countess’s own pianistic skills if she was capable of playing it. (On WoO 65, see Brandenburg & Staehelin, 1984, and Whiting 1991, 79–97.)

The theme for the variations comes from the final number, “Venni, Amore,” in Righini’s XII Ariette italiane, published by Schott in Mainz in 1788. The set is dedicated to Princess Frederica (Friederike) Charlotte of Prussia (1767–1820), the oldest daughter of King Friedrich Wilhelm II. “Venni, Amore” is a simple 16-bar tune to which Righini adds increasingly elaborate vocal embellishments in each of the subsequent five verses. Recalling Schönfeld’s statement that Countess Hatzfeld excelled in passage work and embellishment, we may wonder whether Beethoven might have heard her sing Righini’s arietta and was inspired to produce his own set of variations in her honor.

At least four other published musical works were dedicated to Countess Hatzfeld: a set of three keyboard sonatas by Leopold Kozeluch (Vienna: Torricella, 1784); a set of 12 lieder by Johann Franz Xaver Sterkel (Mainz: Schott, 1789); a set of variations by Neefe on the March of the Priests from Mozart’s Die Zauberflöte (Bonn: Simrock, 1793); and a setting by Sterkel of a Petrarch sonnet (Leipzig: Kühnel, 1808/1809).

Countess Hatzfeld was a subscriber to Mozart’s Lenten concerts in the Trattnerhof in 1784 (Briefe, iii:307), and she is on the list of subscribers (two copies) for Artaria’s first edition in 1795 of Beethoven’s Piano Trios, op. 1.

Countess Hatzfeld’s husband died in Bonn on 16 Sep 1794; this is also the last year for which we have any evidence of her performing (assuming that performances of Axur took place at Auersperg’s that year). Almost nothing is currently known about her life past that point. A notice of bankruptcy proceedings against her was published in the Wiener Zeitung by the court of Lower Austria on 21 May 1800:

⁣   Konkurs gräfl. Hatzfeldscher Gläubiger.
    Von den k. k. ni. öst. Landrechten wird anmit
bekannt gemacht: Es sey von dem Gerichte in die
Eröffnung eines Konkurses über das gesammte im
Lande Oesterreich unter der Ens befindliche be=
weg= und unbewegliche Vermögen der Frau Hor=
tensia Gräfin v. Hatzfeld, gebohrnen Gräfin v. Zie=
rotinn, gewilliget worden. [...]
[WZ, no. 41, Wed, 21 May 1800, 1687]

Bankruptcy, creditors of Countess Hatzfeld.
    It is hereby made known by the imperial royal
state court of Lower Austria: the opening of
a bankruptcy proceeding has been approved by
the court against all movable and immovable
assets in the land of Austria below the Ens of
Frau Countess von Hatzfeld, née Countess
Zierotin. [...]

A notice published a week later refers to her failure to repay a very substantial debt incurred in 1795.

Countess Maria Anna Hortensia von Hatzfeld, née Countess Zierotin, is said to have died on 31 Dec 1813. The place of her death is unknown: a sad end to the life of a brilliant musical talent whose life had intersected Mozart’s.

Reicha’s memoirs contain three other anecdotes about Mozart and his works. One is found in a note about Idomeneo added to the anecdote about Countess Hatzfeld’s performance of “Tutte nel cor vi sento”:

Cet opéra n’a eu qu’une seule représentation depuis qu’il existe. Mozart tenait le piano, tous les acteurs se mirent dedans en éxécutant le quatuor en mib du 3eme acte. Mozart en rit et pour rire plus à son aise, il cacha sa tête sous le piano. Grâce à l’editeur qui a fait graver la partition elle fut conservée à la posterité. [Audéon et al. 2011, 102n45]

This opera has had only had a single performance since it came into existence. Mozart was at the piano, all the actors broke down performing the quartet in Eb in the 3rd act. Mozart laughed about it, and to laugh more comfortably, he hid his head under the piano. Thanks to the editor who engraved the score, [the opera] was preserved for posterity.

The quartet in Act 3 is “Andrò ramingo e solo,” for Ilia, Elettra, Idamante, and Idomeneo. Reicha is of course wrong about the single performance, but the comment would seem to place the anecdote at a rehearsal for the first production in Munich. Idomeneo was first published in keyboard score in 1797 by Schmidt and Rau in Leipzig, on commission from Constanze Mozart; the first edition in full score was published by Simrock in 1805. The anecdote is clearly hearsay.

Reicha also relates an anecdote about Beethoven performing a Mozart piano concerto in Bonn:

Beethoven exécuta à la cour un concerto de Mozart sur le piano, il me prie de lui tourner les feuilles. Les cordes du piano cassent à tout moment, sautent en l’air; les marteaux s’embarassent entre les cordes cassées et Beethoven veut à toute force terminer son morceau, il me prie donc de dégager les marteaux à mesure qu’ils s’arrêtaient et d’enlever les cordes cassées, pour parvenir à tout j’avais plus affaire que lui, car il m’a fallu tourner autour du piano pendant tout le morceau. [Audéon et al. 2011, 102]

Beethoven was playing a piano concerto by Mozart at court; he asked me to turn the pages. The strings of the piano were breaking constantly, flying into the air; the hammers were becoming tangled in the broken strings, and Beethoven wanted to complete his piece at all costs. So he asked me to untangle the hammers as they stopped working and to remove the broken strings. To accomplish all of this I had more to do than he did, for I had to circle the piano during the whole piece.

Assuming this incident actually took place—and it is Reicha’s personal reminiscence, so there is no reason to doubt it—it must have happened in Bonn before Beethoven left permanently for Vienna in Nov 1792. The concerto cannot be identified with certainty, but Beethoven is known to have had the Concerto in D minor, K. 466, in his repertoire, and it is easy to imagine Beethoven breaking strings in that work.

Reicha also writes of attempting to visit Mozart’s grave in Vienna around 10 years after Mozart’s death:

Etant à Vienne, j’ai voulu voir le tombeau de Mozart; on me dit qu’il était impossible d’en retrouver la trace; il n’y avait qu’environ 10 ans qu’il était mort. On l’avait enterré sans le moindre cortège; des polissons criaient: voilà l’ivrogne de musicien que l’on conduit au tombeau. [Audéon et al. 2011, 98]

Being in Vienna, I wanted to see the grave of Mozart; I was told that it was impossible to find any trace of it; it was only around 10 years since he had died. He was buried without the least cortège; the street urchins cried: there goes the drunkard musician being taken to his grave.