Answer: Once Upon a Dream
George Bruns adapted the music for the memorable "Once Upon a Dream" from the "Grande valse villageoise" (literally "The Great Village Waltz" but better known as "The Garland Waltz" in English), from Tchaikovsky's second ballet "The Sleeping Beauty" , or "Spyashaya krasavitsa" (1890), Op. 66. The lyrics ("I -- know -- you; I walked with you once upon a dream...") were written by Jack Lawrence and Sammy Fain. During the dance scene in the forest between Prince Philip and Princess Aurora they are reflected in water as they glide across the full width of the screen, taking advantage of the Super Technirama 70 field of view in what is perhaps the most memorable scene of the movie, other than the climactic final battle. Eric Larson directed the entire forest sequence, including the dance. During this dance, neither of them knows that the other is actually royalty and his/her betrothed, and they fall in love with each other at first sight. When each is told that they are already betrothed to another, each reacts with anger and dismay.
During the final scene, as "Once Upon a Dream" is reprised and the Prince and Princess dance among the clouds, Flora and Merryweather continue their battle for the color of Princess Aurora's dress, changing it during the dance from blue to pink to blue again, back and forth until the very end.