"One Day" is a musical theme composed and conducted by Hans Zimmer for Pirates of the Caribbean: At World's End. Zimmer stated that the second part of the soundtrack serves as the love theme for the film, mainly most of Will and Elizabeth's scenes. It also appears as track twelve on the film's soundtrack, at 4:01 in length.
The track begins with slowly ascending chords and a subtle string ostinato of the second love theme variant, similar to that heard in "Up Is Down". It builds into a strong, slow and regal version of Jack Sparrow's theme from "The Medallion Calls". As the theme ends, a soft string ostinato continues, followed by French horns with a rendition of the primary love theme, followed by its other two variations from the final scene with Will and Elizabeth Turner.It accompanies the scenes following the destruction of the Endeavour in the film.