It's been bugging me for ages. It's the cliche 'romance' music, which is now often used humorously as e.g. two lovers run towards each other, or have a thunderbolt love at first sight type moment. It must have originally been used in a romantic film.
I can only remember the first few bars, but it starts with soaring violins. I have a vague suspicion that it might be by Rachmaninov, but I'm shamefully ignorant about classical music, so take that with a pinch of salt.