Britney Spears will grace the X Factor stage tonight for her first UK television performance in over four years.
The pop singer, who turns 27 on Tuesday, will perform her current single Womanizer, while the five remaining finalists will each cover a classic Britney track.
A representative for Spears said she would only be performing and would not coach the show's contestants, as previous guests have done.
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.
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.
On Monday Spears releases her sixth studio album Circus, and has been on a whistle-stop tour of Europe to promote the record. On Thursday she performed at an awards ceremony in Offenburg, Germany, while last night she sang on the French TV show Star Academy.
Spears 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 something of a fresh start for the singer, who in recent years has hit the headlines for her turbulent private life.
In January 2004 she married a childhood friend in Las Vegas for two days before being granted an annulment.
Later that year she married dancer Kevin Federline, but the pair filed for divorce after two years amid growing concern over Spears' state of mind and her frequent use of alcohol and drugs.
After splitting with Federline she hit the party scene with gusto, being photographed climbing out of cars with and without her underwear.
In February 2007 she walked into a salon in Los Angeles and shaved her head bald, before checking into rehab.
In October 2007 Federline was handed custody of the couple's two children, Sean Preston and Jayden James.
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.