Despite Rebecca being twenty years younger, she soon fell in love with Haydn, as she had previously done with Johann Schroeter, a German composer and pianist that she married 16 years before. There were numerous letters back and forth between the two and Haydn had dinner with her at every opportunity. There was no possibility of marriage between the two as Haydn was already married (in what traditionally has been considered an unhappy one) and divorce was not allowed by the church.
Haydn wrote 45 piano trios in his life. His first trio was written in 1760, the beginning of the Classical era of music that saw the obsolescence of the basso continuo in favor of separate parts for specific instruments. Even with that, the piano dominates as the titles reflect with the piano being the first instrument mentioned: trios for piano, violin and cello. The violin accompanies and on occasion has the melody trusted to it while the cello mainly reinforces the bass line.
But this doesn't mean Haydn's piano trios are fluff. The early ones are simpler in texture and are more like serenades, but Haydn's imagination and skill is used to good effect, especially in the later piano trios. Piano Trio No. 39 is in 3 movements:
II. Poco adagio, cantabile - The gentle second movement is in E major. After the initial statement of the theme by the piano, the violin gets the spotlight in the middle section as the piano and cello accompany.
III. Rondo a l'Ongarese: Presto - After two gentler movements, the finale begins in a breakneck presto tempo. Haydn was the first well known composer to use music based on Hungarian tunes in his compositions, which became something of a fad a few decades later. These tunes aren't so much Hungarian but were derived from itinerant Gypsy musicians who were prevalent in Hungary. Haydn would have come in contact with these Gypsy musicians during his tenure as Music Director at Eszterháza Castle where Gypsy musicians often played. This is some of Haydn's most recognizable music and has been transcribed for other combinations as well as solo piano. The movement is a heavily accented, fierce Gypsy dance that shifts from major to minor that is over in a flash.