My Fair Lady's Alexandra Jay (pictured) joins the cast of Abba musical Mamma Mia! next month, ahead of the record-breaking show's fourth birthday at the West End's Prince Edward Theatre on 6 April 2003.

From 17 March 2003, Jay will play Sophie, the young bride-to-be who gathers her mum's three ex's on a Greek island, on the eve of her wedding, in a bid to find out who her father is. Jay is best known to West End audiences for playing Martine McCutcheon's overworked understudy in My Fair Lady. Since then, she's starred as Sally Bowles in Cabaret at Chichester and was recently seen in Too Marvelous for Words at the King's Head.

Also from 17 March, Samuel Board (Jesus Christ Superstar on tour), making his West End debut, will take over as groom-to-be Sky, Kim Ismay (Sunset Boulevard, Torch Song Trilogy) will be the new Tanya and Tim Wallers will join as Harry. At the same time, Michael Simkins will return to play Sam. Olivier nominees Louise Plowright, Myra McFadyen and Rohan Tickell will continue to play Donna, Rosie and Bill, respectively.

Based on the songs of 1970s Swedish supergroup Abba, Mamma Mia! opened at the West End's Prince Edward Theatre on 6 April 1999 (previews from 23 March) and has recently extended its booking period by another to 27 March 2004. Audiences in London - where, say promoters, a seat has never gone unsold - have just passed the two and a half million mark, equating to more than £80 million grossed at the box office.

Worldwide, Mamma Mia! has so far grossed more than $500 million. The musical opened on Broadway in October 2001, one of nine productions currently playing around the globe.

Mamma Mia! is fashioned around the hits (written by Benny Andersson and Bjorn Ulvaeus) of 1970s Swedish supergroup, including such disco classics as "Dancing Queen", "Thank You for the Music", "Take a Chance on Me" and the title song. The show has a book by Catherine Johnson, is directed by Phyllida Lloyd and designed by Mark Thompson.

- by Terri Paddock