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Party princess: Britney Spears hitches up her dress  as she celebrates her 27th birthday with a trip to Club Tenjune in New York

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Falling out? Britney’s lacy bra was on show under her low-cut dress

Miss Spears was also celebrating the launch of her new album, Circus, in what was a rare appearance on the club scene.

After a very public breakdown earlier this year, Miss Spears was admitted into a Los Angeles psychiatric ward and her father Jamie was made a ‘ conservator’ to look after her life.

Since then, the singer has been recording new music and getting back in shape for the release of Circus on Monday. Her comeback has hit a few hiccups, however.

Expectations were high for her appearance on Saturday’s X Factor show, where she performed hit single Womanizer for the studio audience.

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Chance to shine: Britney switches on the lights of the New York Christmas tree at the Rockefeller Centre

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In the spotlight: Britney speaks on stage during the pretaping of 76th Rockefeller Centre Christmas tree lighting ceremony

But suspicions that she had failed to sing live, and that her microphone was just a prop, were confirmed when host Dermot O’Leary had to share his with her during an interview.

There was a sense of deja vu a few days later when Miss Spears performed songs from her new album in front of millions of viewers on U.S. TV show Good Morning America.

Wearing a ringmaster’s costume, and accompanied by clowns, jugglers and performers dressed as animals, she lip-synched her way through the title track from Circus.