Manager Scooter Braun's birthday party invites read like a list of who's who in Hollywood: Justin Bieber (naturally), Usher, Mary J. Blige, Adam Levine, Kim Kardashian, Jaden Smith, Rita Wilson, Wilmer Valderrama, and Nicky and Paris Hilton.
It's no surprise though, considering Scooter is credited with "discovering J.B." and counts Usher as his "best friend."
What was surprising were the amazing impromptu performances that went down thanks to Scooter's talented guests.
Here's a rundown of what SheKnows saw:
The bash began with cocktails, beer pong and Pinkberry on the roof of the Music Box in Hollywood... that's right, beer pong! Besides watching celebrities engage in college-age antics, guests were also entertained by acrobatic circus performers, midgets serving mini drinks and elaborately dressed fortune tellers.
After the pre-party, Bieber and the rest of the partygoers were led downstairs to the concert hall where the spotlights turned on Usher. He grabbed a mic, got on stage and started singing!
Shortly after, the Biebs jumped up as well, and dropped his hits, Baby and Never Say Never. But Bieber wasn't alone, Will Smith's son Jaden joined him on stage and the crowd went wild.
The night's entertainment wrapped up with MC Hammer bringing it back with Too Legit to Quit and Maroon 5's Adam Levine singing This Love.
It's going to be hard for any Tinseltowners to top this party, but we'll bet coast-to-coast birthday queen Paris Hilton is already planning her retaliation for next year!