Birthday girl Britney parties with Paris - as rumours grow that she is pregnant

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.

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

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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.

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.

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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.

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.

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"It doesn't look good, does it? She loses Sean and Jayden and then has a dalliance with someone she hardly knows.

"She gets lonely and needs male attention, so she goes and does silly things. This is the perfect example."

Britney has denied that she is pregnant, claiming the rumours are "completely fake".