Britney Spears celebrate her birthday with Paris Hilton

Party girls: Paris joins Britney as she celebrates her birthday

It looks as though troubled singer Britney Spears is back to her old ways as she spent the night celebrating her birthday with friends in Beverly Hills last night.

The pop star, sporting eye-catching blonde hair extensions, took a break from her bitter custody battle to party with socialite heiress Paris Hilton and Britney's cousin Ali Sims.

Wild girls: Paris and Britney party together

As the singer danced the night away, rumours continued to grow that Britney is expecting her third child.

A source close to the singer claimed she is in fact pregnant but keeping the news a secret following her divorce from ex-husband K-Fed, with whom she already has two children.

Girls gone wild: Paris and Britney rekindled their friendship during the night out

It has already been claimed that the star has already had her first ultra-sound scan but withheld the news from her family as she is still involved in a custody battle over sons Sean Preston, two, and Jayden James, one.

A pregnancy would be difficult for Britney, as she is struggling to prove to the court that she is a responsible mother after regularly failing to turn up for mandatory drug tests. Britney and cousin Ali Sims celebrate her birthday in Beverly Hills

A source told the News of The World: "She's very angry that it has come out like this. She's shocked because the pregnancy is the last thing she needs right now.

"She had the scan last month and only told close friends the result. Even her family were out of the loop."

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Earlier this week, Britney's on-off love interest music producer Jonathan 'J.R.' Rotem allegedly confirmed the news, telling a reporter from American magazine InTouch: "It's true."

However, fresh reports claim the singer is expecting a child after a brief fling with a dancer called Chuck.