I stumbled across this remarkable song and decided to do a little cover. Unexpected Song is a 1984 song from the musical Song & Dance originally sung (on Broadway) by Bernadette Peters. The music was written by Andrew Lloyd Webber, with lyrics by Don Black.
A single was released by Sarah Brightman. Originally released by Marti Webb and Justin Hayward as a duet in 1981 the song had new lyrics penned for the original 1982 production of the show and was re-titled "When You Want to Fall in Love".
The original lyrics were re-instated when the show was re-written for Brightman's run. It was later used in Lloyd Webber's and Black's reworking of the show, returning to the original album title of Tell Me on a Sunday. The single peaked at #76 on the UK Singles Chart. - from Wikipedia