Britney Spears sang her latest hit on the X Factor stage during her first UK television performance in over four years.
The pop singer, who turns 27 on Tuesday, mimed her way through her latest single Womanizer after the five remaining finalists each covered a classic Britney track.
Spears, who was dressed all in black, with hotpants, fishnet tights and knee-high boots, did not coach the show's contestants, as previous guests have done.
It has been reported Spears travelled with a 45-strong entourage of stylists and security. And reports claimed she is said to have banned contestants and judges from approaching her.
But the judging panel gave her a standing ovation along with an excited crowd.
On Monday, she releases her sixth studio album Circus, and has been on a whistle-stop tour of Europe to promote the record.
Earlier, Alexandra Burke, who sang 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 performed Sometimes, Ruth Lorenzo - who was later voted off the reality show - sang I Love Rock 'n' Roll, Diana Vickers sang I'm Not A Girl, Not Yet A Woman and JLS took on Baby One More Time.
Lorenzo became the eighth contestant to be booted off the show but bowed out gracefully after receiving the least amount of public votes.
She said: "I fought with all my heart, with everything I had. And this doesn't end here. This is the beginning of my dream. All I can say is thank you so much. I never ever dreamed of this ever."
With judge Simon Cowell looking on wistfully, she then belted out another performance of Bon Jovi's Always.
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