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Demi Lovato is 21 - see 21 photos of birthday girl's cutest smiles

Demi Lovato poses with fellow 'X Factor' judge Simon Cowell at FOX's Upfront Presentation in New York on May 13, 2013. <span class=meta>(Kristina Bumphrey / Startraksphoto.com)</span>
March 27, 2014 3:33:58 PM PDT