Nick Jonas turns 21; parties at Vegas with girlfriend

Nick Jonas is officially 21. Now that he's entered legal age, the former Jonas Brothers member hit the party scene at Las Vegas' XS nightclub!

Nick was joined by his brothers, some pals and  his girlfriend, Miss Universe 2012 Olivia Culpo. The flock partied the night out in style with champagne, music and a massive birthday cake courtesy of the XS nightclub.

Throughout the night, the singer and his girlfriend looked all very sweet and seems to be having so much fun celebrating Nick's new-found adulthood.

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Happy Birthday Nick!