The Immortal Beloved (German "") is the addressee of a love letter which composer Ludwig van Beethoven wrote on 6 or 7 July 1812 in Teplitz (then in the Austrian Empire, now in the Czech Republic). The unsent letter is written in pencil on 10 small pages. It was found in the composer's estate following his death and is now in the Berlin State Library.

Beethoven did not specify a year or a location. In the 1950s an analysis of the paper's watermark yielded the year, and by extension the place of the letter. Scholars disagree about the intended recipient of the letter. Two people favored by most contemporary scholars are Antonie Brentano, , , supported by Cooper (2000), and , contested by , Tellenbach (1983, 1987, 1988, 1993–1994, 1998), Beahrs (1972, 1986, 1988, 1993), , , , , Steblin (2007), and ; numerous refutations in The Beethoven Journal 16/1 (Summer 2001), pp. 42–50. and Josephine Brunsvik.; ; ; Massin (1967, 1970); ; Tellenbach (1983, 1987, 1988, 1999); Beahrs (1986, 1988, 1993); ; ; Noering (1995); Steblin (2002a, 2007, 2009b). (Other possibilities include Johanna van Beethoven, Julie ("Giulietta") Guicciardi, Therese Brunsvik,, Thomas-San-Galli (1909, 1910), , Amalie Sebald,Thomas-San-Galli (1909, 1910); see: Dorothea von Ertmann, Therese Malfatti, Anna Maria Erdődy, and Bettina von Arnim.)

Text analysis After Schmidt-Görg (1957) published 13 then-unknown love letters by Beethoven to Josephine Brunsvik, it became clear that the one to the "Immortal Beloved" was not the only love letter authored by him. That Josephine could have been the unknown woman was subsequently suggested by analyses of similarities in wordings and phrases between earlier letters (from 1804 to 1809) and this mysterious one from 1812, mainly in the monographs by Massin (1967, 1970), and ):Letters in the following quoted from .

My angel (used again towards the end of this letter): see "farewell angel – of my heart – of my life." (#219, April 1805) – this also uses the intimate German "Du" ("Leb wohl Engel"); "farewell angel of my heart" (#220, April/May 1805). My everything, you – you – my life – my everything: see "you – you – my everything, my happiness ... my solace – my everything" (#214, 1st quarter 1805); "dear J. everything – everything for you" (#297, after 20 September 1807). Esterhazy: This Hungarian Prince was well known to the Hungarian Brunsviks. remain my faithful only, your faithful ludwig, since you know my faithfulness to you, never can another own my heart, never – never, never misjudge the most faithful heart of your beloved L., forever thine, forever mine, forever us: see "Long – Long – may our love last – it is so noble – so much founded on mutual respect and friendship – even great similarity in so many things, in thoughts and feelings – oh let me hope that your heart – will continue to beat for me for a long time – mine can only – stop – to beat for you – if – it does not beat any more – beloved J" (#216, March/April 1805); "your faithful Bethwn" (#279, May 1807); "your faithful Bthwn, eternally devoted to you" (#294, 20 September 1807). Clearly refers to a pre-existing long-term relationship. You are suffering you my dearest ... you are suffering – Oh, wherever I am, you are with me: Josephine was not only frequently ill, but especially desperate around that time because her husband had left her. but – but never hide yourself from me: During 1807, Josephine began to withdraw from Beethoven due to family pressure; she was not home when Beethoven came to see her (see #294 and #307). I must go to bed : the heavily crossed-out words are probably the strongest indication that their love had been consummated (and may explain the birth of Minona, Josephine's seventh child, exactly nine months later).

The period of speculation (1827 to 1969) In his 1840 biography of Beethoven, Anton Schindler named Julie ("Giulietta") Guicciardi as the "Immortal Beloved". But research by Tellenbach (1983) indicated that Giulietta's cousin Franz von Brunsvik may have suggested her to Schindler, to distract any suspicion away from his sister Josephine Brunsvik, with whom Beethoven had been hopelessly in love from 1799 to around 1809/1810. La Mara (1909) published Therese Brunsvik's memoirs, which show her full of admiration and adoration of Beethoven. This, together with interviews of some of the Brunsvik descendants, led her to the conclusion that Therese must have been the "Immortal Beloved".

At first, most researchers, including Alexander Wheelock Thayer, also believed Therese was the "Immortal Beloved". Thayer thought the letter must have been written around 1806–07. Thomas-San-Galli (1909, 1910) checked out the official listings of guests in Bohemia, and at first (in 1909) concluded that Amalie Sebald was the "Immortal Beloved". Sebald was definitely not in Prague at the beginning of July, 1812, and Cooper consequently ruled her out as a possibility. Thomas-San-Galli then speculated (in 1910) that it might instead have been Therese Brunsvik, whom he believed could have secretly traveled to Prague.

Doubts were raised by , who ruled out Therese Brunsvik, (the "Louis" mentioned by Therese in her diary was, in fact, Count Louis Migazzi) and by Unger (1910) against Amalie Sebald. A summary of the older literature can be found in Forbes's work.

There was also a forged Beethoven letter by Paul Bekker in Die Musik. But it was already shown to be a hoax by —a last-ditch effort to salvage the discredited Guicciardi hypothesis.

The date of the "Immortal Beloved" letter—6/7 July 1812—has meanwhile been firmly established, not only by watermarks and references, but also by a later letter by Beethoven to Rahel Varnhagen, which suggests he must have met his "Immortal Beloved" on 3 July 1812: "I am sorry, dear V., that I could not spend the last evening in Prague with you, and I myself found it impolite, but a circumstance I could not foresee prevented me."

La Mara (1920), after discovering more letters and notes in the Brunsvik estates, was now convinced "that ... Josephine widowed Countess Deym was Beethoven's 'Immortal Beloved'".

, for the first time, published Therese's diary notes ending in 1813; some were known already to . and concluded that Beethoven was in love with Josephine, but nonetheless he tended towards Therese as the "Immortal Beloved".

evaluated more of the documents in the Brunsvik estates, and even though he thought that Rahel Varnhagen was behind the "Distant Beloved", he concluded that the "Immortal Beloved" must have been Josephine mainly because her daughter Minona was born exactly nine months after the encounter with Beethoven and her husband Baron Stackelberg was away. Kaznelson arrived at his conclusion even though in Zurich, owner of the "13 Letters" after World War II (see following), would not allow him access to them.

Editha and Richard Sterba, using psychoanalysis, argued for Beethoven's nephew Karl as the "Immortal Beloved".; refuted by

Steichen identified Marie Erdödy to have been a lifelong beloved of Beethoven, and thus she could also be the "Immortal Beloved".; refuted by

George R. Marek (1969) argued the case for Dorothea Von Ertmann.; refuted by .

The discovery of Josephine Brunsvik (1957–1999)

Schmidt-Görg published 13 heretofore unknown love letters by Beethoven to Josephine Brunsvik (and a draft letter by him that survived as a copy by Josephine), that could be dated to the period from 1804 to 1809/10 when she was a widow after the early death of her first husband Count Deym. Schmidt-Görg dismissed Kaznelson's discoveries as "sensationalist". Goldschmidt explains why the German Beethoven scholarship was so reluctant to accept Kaznelson's theory (already published before these "13 letters"): "The fact that, as a result of this meeting, they had to take a natural daughter into account, appeared so venturesome to the professional world that the resistance to the Josephine hypothesis stiffened noticeably." Schmidt-Görg (1957) believed that with the last letter (which he still thought to have been written in 1807—not 1809) and with Josephine's marriage to Baron Stackelberg (in 1810) the love relationship was terminated.

Ley (1957) saw it differently:

, still very much a "standard" German biography of Beethoven, followed Kaznelson regarding Josephine being his "only love", likewise Dahlhaus who concluded that "internal evidence" points to Josephine.

The French authors Jean and Brigitte Massin (1967) identified Josephine as the "Immortal Beloved", mainly based on comparisons of the "Letter to the Immortal Beloved" with the earlier 14 (15) love letters: "The letter to the 'Immortal Beloved'... not only uses similar wording, but also emphasizes his long-time faithfulness to his one and only Beloved." In addition, with regard to traces in Beethoven's compositions, the "Massins argue that... the presence of Josephine in Beethoven's life left traces in his music... From the standpoint of music theory, the connections make eminent sense.", elaborated by

After Massin & Massin (1967) and , Tellenbach (1983, 1987, 1988, 1999) argued extensively the case for Josephine, based on many newly discovered documents, like Therese's later diary notes, e.g., on the discovery of the "Three letters by Beethoven... they must have been to Josephine whom he loved passionately."

"Beethoven! It is like a dream, that he was the friend, the confidant of our house—a beautiful mind! Why did not my sister Josephine, as widow Deym, take him as her husband? Josephine's soul-mate! They were born for each other. She would have been happier with him than with Stackelberg. Maternal affection made her forgo her own happiness." She could not contemplate marrying Beethoven, a commoner, for the simple reason that she would have lost the guardianship of her aristocratic children.

Again Therese on Beethoven: "How unhappy, with such intellectual talent. At the same time Josephine was unhappy! —both together they would have been happy (perhaps). What he needed was a wife, that's for sure."

"I was so lucky to have been acquainted with Beethoven, intimately and intellectually, for so many years! Josephine's intimate friend, her soul mate! They were born for each other, and if both were still alive, they would be united."

Goldschmidt's evaluation of the Josephine hypothesis: "Without conclusive proofs of the opposite one should no longer want to part prematurely with the increasingly justified assumption that the 'Immortal Beloved' could hardly be anyone else but the 'Only Beloved'."

Josephine's candidacy as the "Immortal Beloved" was contested by , mainly in response to Massin (1967, 1970), and .

Antonie Brentano and other alternatives (1955–2011)

In 1955, the French scholars Jean and Brigitte Massin noted that Antonie Brentano was present in Prague and Karlsbad at the time and proposed her as a possible candidate for the "Immortal Beloved":

"The assumption that it could have been Antonie Brentano, is both tantalizing and absurd." They then argue:

"Tantalizing" is the assumption, because Beethoven and Antonie, since her return to Vienna, were "on friendly terms", In the summer of 1812 he lived in the same hotel in Franzensbad as the Brentanos, and He had dedicated in the same year to her daughter Maxe a one-movement trio. "Absurd", they argue, is the assumption because of Beethoven's lasting friendship with Antonie's husband, Franz, He borrowed money from him, and "The many letters he wrote Antonie prove that a true and deep but—due to mutual restraint—nevertheless only formal friendship existed between them and Beethoven always seems to perceive Franz, Antonia and their children as an inseparable unity."

There was four years later also a claim by Japanese author Yayoi Aoki who had "discovered" Antonie. However, this had not been noticed outside Japan. She also published her findings again in a recent book in German.