Promise To Be True is an unreleased song recorded on 30 April 1983 at Prince's Kiowa Trail Home Studio in Chanhassen, Minnesota, the same day as basic tracking for Sex Shooter. It was intended for Vanity 6's planned second album, although it is unclear if Vanity ever recorded vocals for it. Dez Dickerson worked on it in May 1983, but when Vanity decided in August not to participate in the Purple Rain movie, the song was shelved for the time being.
The track was worked on further (or perhaps re-recorded) in early 1987, at Prince's Galpin Blvd Home Studio,Chanhassen, MN, USA, for use by American blues singer-songwriter Bonnie Raitt, during a short-lived collaboration between the two artists. It is not clear if she recorded lead vocals for the track, however. Although Prince offered four songs to Bonnie Raitt (I Need A Man, Jealous Girl, Promise To Be True and There's Something I Like About Being Your Fool), it is unclear whether this collaboration was intended to lead to an album or to a particular project. The track remains unreleased.