Emily Zarevich at JSTOR Daily:
It’s one of the great mysteries of music history, as high in the ranks as “Who wrote the Renaissance lover’s tribute ‘Greensleeves’” and “How did Amadeus Mozart really die?” In eighteenth- and early nineteenth-century Europe, correspondence was a private means of communication, and some clandestine love affairs conducted in secret succeeded in evading confirmation from even the most determined detectives. Which is why the world is still wondering, centuries after the question was first asked, “Who was Beethoven’s ‘Immortal Beloved?’”
More here.