This is an oldie -- maybe 1960s or 70s -- about a Confederate spy who made his way north with a northern theatre group. Inevitably he and the star fell in love, the war intervened, and she was singing at Carnegie Hall (I think) when the end of the war was announced. She managed, with a little help from her co-star, to get the audience singing I Wish I Was In Dixie in honour of the losers.
Can anybody recall it? Movie title, stars, date, anything at all, really?