Britney Spears celebrates birthday with Tinashe and fans at KIIS-FM's Jingle Ball in L.A.
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Pop superstar Britney Spears worked on her birthday on Dec. 2, but still made the most of the night with fans and Tinashe. Both singers premiered their duet version of "Slumber Party" live for the crowd at KIIS-FM's Jingle Ball.

Spears was one of the headliners for this year's Jingle Ball show at L.A.'s Staples Center alongside acts like Justin Bieber, Bruno Mars and Fifth Harmony. For her set, Britney ran through many hits, including "Stronger," "You Drive Me (Crazy)," "Toxic" and "Make Me..." She closed out her section with a surprise, performing "Slumber Party" with Tinashe for the first time ever. The two slinked across the stage like in the sexy music video and appeared to have the time of their lives together. Spears and Tinashe put the party in "Slumber Party" for the sold-out crowd.

Following the "Slumber Party" performance, KIIS-FM's Ryan Seacrest emerged and encouraged the whole venue to sing "Happy Birthday" to Spears. The crew wheeled out a lit-up birthday cake as the words to the tune filled the air. Britney got a surprise herself that night with the impromptu celebration with thousands of people (and Tinashe playfully bowing to the pop princess).

"Slumber Party" featuring Tinashe is now available on iTunes and Apple Music. Spears' Glory album was released back in August and hit No. 3 on the Billboard 200 chart.