During an appearance on The Ellen DeGeneres Show, Sia premiered "Unforgettable", the song she recorded for the movie Finding Dory Most of us will recognise the song, written by Irving Gordon and first performed by Nat King Cole. The singer's daughter, Natalie Cole, recorded a cover in 1991. Following the example of those before her, Sia pours out her soul as she belts the jazzy tune.It was a fitting setting for the debut, since DeGeneres stars in the Finding Nemo sequel. The movie picks up after Nemo is found and tells the story of Dory, the trusty regal blue tang who helps find him.Pixar also plans to introduce a few new characters , including Dory's parents, played by Eugene Levy and Diane Keaton. Like the original film, Finding Dory centres on a search — but this time, it's for Dory's long-lost family.Who knows if it'll live up to Finding Nemo, but at the very least, it's got some great musical accompaniment.