Britney Spears will appear on the X Factor tonight for her first UK television performance for more than four years.
The pop singer will perform her current single Womanizer, while the five remaining finalists will each cover one of her songs.
Her appearance is part of a whistle-stop tour to promote the release of her sixth studio album, Circus, which is out in the UK next week.
Spears, who is 27 on Tuesday, recently announced two concerts in London next summer as part of her world tour. She is scheduled to play at the O2 Arena in London on June 3 and 4.
The new album and tour mark a comeback for the singer, who in recent years has hit the headlines for her turbulent private life.
In January this year police took her to a psychiatric hospital, fearing she would harm herself. Her parents said at the time that they believed her life was at risk.
A representative for Spears said she would only be performing on X Factor and would not coach the show's contestants, as previous guests have done.
Contestant Alexandra Burke, who will be singing Toxic, said: "When I was nine, Britney brought out Baby One More Time, and I loved her.
"I'm very excited about meeting her. This is the Britney we all know and love.
"I hope I can do my Britney song justice, with my own twist."
Eoghan Quigg will perform Sometimes, Ruth Lorenzo will sing I Love Rock 'n' Roll, Diana Vickers will sing I'm Not A Girl, Not Yet A Woman and JLS will take on Baby One More Time.
The 16-year-old pop star and actress Miley Cyrus will also perform on the show.
Previous stars to have appeared on this year's X Factor include Take That, Mariah Carey and Girls Aloud.