these days. The celebrated her 41st birthday on the evening of Saturday, September 10 with a star-studded party at a mansion in Bel-Air (her actual birthday was on September 4). While the guests were all over the place (Beyoncé can invite whoever she wants!), there was certainly a consistent element in everyone's outfits: sparkle. According to Megan Fox, who showed up with fiancé Machine Gun Kelly on her arm, the theme was roller disco, which checks out.