Usher 'OMG' Live at SummerTime Ball ft will.i.am and joined on stage by JUSTIN BIEBER
Usher performs recent hit 'OMG' in front of 70,000 fans in London's Wembley Stadium and is joined on stage by special guest's will.i.am and then the loudest scream of the day goes to Justin Bieber as he makes his way onstage to bust some moves. As
