The first ever Best Song Oscar went to Con Conrad and Herb Magidson for “The Continental,” from The Gay Divorcee, the film version of the stage music Gay Divorce, the first in a proud tradition of songs-added-to-existing-scores to win.
Gay Divorce had a score by Cole Porter, but back in those days it was pretty common for film studios to hire new writers to add songs to film adaptations, even when you’re working with source material by a genius like Cole Porter.