While several musicians hit the stage at Cardiff Millennium Stadium this past weekend for the "Michael Forever" tribute concert, only one has left us asking, "what happened to her?" Christina Aguillera performed for the show, but it wasn't her performance that many are talking about around the water cooler today. Once known for her slim and toned figure, Aguillera is a long way from those days.Aguillera was one of several artist to hit the stage in the "Michael Forever" tribute. She sang "Dirty Diana" and "Smile" for the tribute. However, the big surprise of the evening came when Michael's kids hit the stage in the salute.