The winner of Any Dream Will Do will be singing songs from the musicals with loads of big name stars at a gig being organised by Princes William and Harry.
Lee Mead, who is the new lead in Joseph and his Technicolor Dreamcoat, will be joined by two former Josephs - Jason Donovan and Donny Osmond - and others.
The mix of songs - called a musicals medley - is being put together by Sir Andrew Lloyd Webber.
The Princes are holding the concert at Wembley Stadium in memory of their mum.
Princess Diana died in a car crash 10 years ago. The gig is being held on 1 July, which would have been her 46th birthday.
The concert will be a celebration of Princess Diana's life
The line-up also includes new bands, who the Princes think their mum would have liked, and some of her fave acts, like Elton John and 1980s band Duran Duran.
The concert will raise money for several of Diana's favourite charities as well as two of the princes' own charities - Centrepoint and Sentebale.
A memorial service for family and friends will be held on 31 August, exactly 10 years to the day after Diana's death.