OK, I admit it. This is my second go on this. I can't help being lachrymose!
Schubert's Adagio D.956 in C when performed by the Melos quartet plus the great cellist Mstislav Rostropovich. They play it more slowly and thus more movingly than most others. The music was used in the film Conspiracy. Schubert was only 31 when he died in 1828 and never heard this work performed. And if that isn't sad I don't know what is!