Britney Spears was a surprise guest at a party hosted byNicki Minajin West Hollywood.

A witness told E! Online that the crowd went wild when the Hold It Against Me singer joined Nicki on stage at the rapper’s post-concert bash at The Factory nightclub: "[It] was complete pandemonium. Six people were carried out after hyperventilating. They literally fainted when Britney walked onto the stage where Nicki was hanging.

"People were crowd surfing to get to the stage. Screams were so loud for Nicki and Brit you couldn't hear the music. Bouncers couldn't hold the crowd back."

Britney later tweeted about how much she enjoyed the night: "Hanging with my girl Nicki Minaj at her after party at The Factory. Love you girl.”

The Moment 4 Life star was recently announced as the opening actfor Brit’s Femme Fatale tour. The ladies have also joined up with Ke$ha on a remix of Britney’s hit Till The World Ends.

The Pink Friday diva kicks things off with an aggressive rap: "Chimpanzees is hating, but I take it all in stride/Put her in a jungle with bananas on the side/Told you they'd revive your career, but somebody lied/I ain't talking poultry when I say this chicken's fried!"

It’s Ke$ha’s turn next – the Tik Tok star sings the first chorus before the Young Money MC does the introductions: "It's Britney, bitch. I'm Nicki Minaj and that's Ke$ha!"

Multi-talented Ke$ha co-wrote Till The World Ends with pop maestro Max Martin.