Hearing Coldplay perform and rubbing elbows with former President Bill Clinton is a pretty decent way to ring in your 35th birthday. For Beyoncé, it was just the tip of the iceberg.The pop star kept her birthday celebrations going all Labor Day weekend long. On Monday night, she rounded up her celebrity guests for a Soul Train-themed soiree complete with '70s-inspired costumes, dance-offs, and a birthday cake topped with sparklers. Us Weekly reports that Alicia Keys, Solange Knowles, Usher, Kelly Rowland, Michelle Williams, Janelle Monáe, Chanel Iman, Kendrick Lamar, Diddy, and Chance the Rapper were among the party guests in attendance. Taking a page out of her former character Foxxy Cleopatra 's book, Bey hit the dance floor in a disco-inspired getup that was half hot pants, half bellbottoms. Jay Z dutifully played along in a Jimi Hendrix-style wig. We've said it before and we'll say it again: #relationshipgoals.