Tori Amos's long-awaited musical will open at the National Theatre later this year – two years after it was first announced.

The singer-songwriter, who had a number one hit with Professional Widow in 1996, has written music and lyrics for The Light Princess which is based on a story by Scottish writer George MacDonald.

The show was originally scheduled to appear at the theatre, on London's South Bank, in April 2012, and will now appear some time in October.

National Theatre director Nicholas Hytner said the delay was down to the fact musicals "take a hell of a lot of writing and developing".