Gah! I can't remember the name!
Whatever it is: it's exceedingly sad, then entirely not, great juxtaposition.
Edit: AH HA! Moonlight Sonata!! Beethoven. Or more correctly Piano Sonata No. 14 in C-sharp minor "Quasi Una Fantasia", Op. 27, No. 2 by Ludwig van Beethoven, but you get the point.
Youtube Link.
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