Past stars of West End stage musical Chicago are uniting for a performance to mark its 10th anniversary.
Osbourne is currently starring as Mama Morton
Denise Van Outen, Ute Lemper and Ruthie Henshall will be among the performers at the London gala on 5 December.
The event will be co-hosted by Andrew Lloyd Webber, actress Liz Hurley and Oscar winner Julian Fellowes.
The show opened at London's Adelphi Theatre in 1997, and has played to around 4.5 million people during its run of more than 4,000 performances.
It transferred to the Cambridge Theatre last year.
Other performers from the rapidly-changing cast who have been confirmed for the charity gala include former Blue star Duncan James and X Factor singer Brenda Edwards.
Based on the 1926 play of the same name, the musical version of Chicago made its debut on Broadway in 1975, with choreography by Bob Fosse.
The story focuses on would-be starlet Roxie Hart who is hauled into prison for killing her lover.
Denise Van Outen played Roxie Hart in both the UK and US
After hiring hotshot lawyer Billy Flynn, she becomes a press sensation - much to the disgust of fellow inmate and murderess Velma Kelly.
A successful Broadway revival in 1996 led directly to the West End production, and further shows are currently planned for Japan, South Korea and Denmark.
The latest cast member to make her debut in London is Kelly Osbourne, whose maiden performance as prison warden Mama Morton was greeted warmly on Monday night.
Actors who have graced the stage in the lead male role of Billy Flynn during the past decade include David Hasselhoff, singer Marti Pellow and Torchwood star John Barrowman.
The show has become known for "stunt casting" - putting well-known names in lead roles to generate box office interest.