After Beethoven’s death in 1827, an unsent love-letter was discovered in a hidden compartment of his desk. For centuries, scholars have tried to guess who the intended recipient of the love letter was, and if it resulted in an affair.
Sources:
https://www.cpr.org/2020/09/22/the-2-women-who-could-be-beethovens-immortal-beloved/
https://books.lettersofnote.com/products/letters-of-note