The song began as the Spanish bolero Cuando vuelva a tu lado, written by Maria Grever in 1934, before Stanley Adams added English lyrics the same year. As What a Difference a Day Made it became a jazz and pop standard recorded by many artists, with Dinah Washington's 1959 version winning a Grammy and becoming the best known recording. Its hopeful theme and instantly recognisable title line have kept it in films, adverts and online edits where a transformation needs a classic, emotional shorthand.