Beethoven took Countess Giulietta Guicciardi on as a pupil in around 1801 and soon fell in love with her. His Sonata Op. 27 no. 2, 'Moonlight Sonata' is dedicated to her...
Sonata Op. 27 no. 2 was published in 1802 under the title Sonata quasi una Fantasia, but is known today as the Moonlight Sonata after the German music critic Ludwig Rellstab wrote that it reminded him of the moon setting over Lake Lucerne.
It is certain that Beethoven proposed marriage to Giulietta, and that she was inclined to accept. One of her parents was in favour of the match.
But the other - probably her father - forbade her to marry a man "without rank, fortune or permanent engagement; a man, too, of character and temperament so peculiar, and afflicted with the incipient stages of an infirmity which, if not arrested and cured, must deprive him of all hope of obtaining any high and remunerative official appointment and at length compel him to abandon his career as the great pianoforte virtuoso". (Thayer's Life of Beethoven)
Giulietta married instead Count Wenzel Robert Gallenberg, a prolific composer of ballet and occasional music, on 3rd November 1803. The newly married couple left for Italy and were in Naples in the spring of 1806 - there Gallenberg composed music for the fête celebrating Joseph Bonaparte's assumption of the crown of the two Sicilies. In late 1821 he was made an associate director of the Royal Imperial Opera in Vienna, and the couple returned to Vienna, but there is no evidence that Beethoven renewed his friendship with his old flame.
This would be the extent of my knowledge of Giulietta Guicciardi, were I not to have made the acquaintance of Lady Chelwood, widow of a former member of the House of Lords, now living in Sussex in England.
Pia Chelwood, who is Austrian, is directly descended from Giulietta. She informed me that Gallenberg was impotent and that Giulietta had a lover by whom she had several children. Pia is a direct descendant of Giulietta's illegitmiate son! At her home she has a white marble bust of Giulietta that was sculpted from life. Bonnie and I visited her there, where I took this picture of Pia with the bust of her ancestor.