The pop star rocks the mic in L.A. during rehearsals for Sunday's American Music Awards. Plus: Heidi Klum, Matthew & Levi, Rob & Taylor and more

WHO'S THE MAN!

Diddy steps up to celebrate a V.I.P. – himself! – during his belated 40th birthday bash at New York City's Plaza Hotel on Thursday. The music mogul's star-studded party drew guests including Kim Kardashian, Jay-Z and Martha Stewart.