Antonie Brentano was almost certainly the Eternally Beloved, the only woman as far as we know ever to return Beethoven's love.
The evidence is contained in the famous letter Beethoven wrote in Teplitz in July 1812 to the woman with whom the week before he had had a brief affair in Prague. In this letter - and its two postscripts - there are no certain clues to her identity, and he never uses her name.
However it is clear from the letter that the woman in question, to be identified, needs to satisfy three conditions. She must be a woman well known to Beethoven in Vienna; she must have been in Prague in the first week of July 1812; and she must have been in the Bohemian spa town of Karlsbad in the weeks following.
Only one woman - to our knowledge - satisfies all three conditions: Antonie Brentano.
Antonie, daughter of a diplomat, was born and raised in Vienna. Her childhood was not particularly happy. Her mother died during an influenza epidemic when Antonie was just eight years of age. After that, her father put her into a convent school as a boarder, where she stayed for seven years.
An attractive woman, by the time she was 18 four suitors had come forward to propose marriage to her. She was herself in love with one of them, but her father had other plans for her. He arranged for her to marry Franz Brentano, a wealthy Frankfurt merchant 15 years her senior.
Franz was a kindly and sympathetic husband, allowing his homesick wife to return frequently to her beloved Vienna.
It is not clear exactly how or when Beethoven first met Antonie. He certainly knew her by 1811, when she makes a reference to him in a letter to her brother-in-law. It is possible he met her through Bettina Brentano, half-sister of Franz, with whom he was already acquainted -- Bettina, a friend of Goethe , would later arrange for Beethoven to meet the great German dramatist.
Antonie suffered from frequent bouts of illness. During one such period Beethoven would go to her house and play the piano in the anteroom outside her bedroom. On one occasion, Beethoven was playing so furiously that Antonie's young daughter Maximiliane ran in and poured a pitcher of water over his head.
Antonie, with her husband and one of her children, arrived in Prague on 3rd July 1812, on their way to Karlsbad. Beethoven had arrived two days earlier. The love affair took place on the night of 3rd July; Beethoven left for Teplitz the next day.
Beethoven saw Antonie in the weeks following in Karlsbad and Franzensbad. But there is no evidence he ever saw her again after that. By the time he arrived back in Vienna -- via Linz where he had gone to try to stop his brother Johann marrying his housekeeper -- the Brentanos had left Vienna for Frankfurt.
Antonie had a sad life. She outlived her husband and all but one of her children. Beethoven dedicated the great Diabelli Variations Op 120 to her. There is evidence he intended dedicating his two final Piano Sonatas Opp 110 & 111 to her. He almost certainly wrote his song cycle, An die ferne Geliebte [To the Distant Beloved], with her in mind.
Beethoven dedicated the Piano Sonata Op 109 to Maximiliane, and also wrote a one-movement Piano Trio for her, WoO 39.
On learning of Beethoven's death, Antonie began noting down the names of her friends who had died. By the end of her long life the list ran to many pages. The first entry read: "Beethoven, 26 March 1827".
The portrait shown here (at top of page) was originally believed to be of Giulietta Guicciardi , but the American Beethoven scholar Maynard Solomon has identified it almost certainly as Antonie Brentano.