No that's not karaoke -- that's really Justin Bieber and Carly Rae Jepsen doing a duet! The Canadian cuties got together to serenade a wild crowd of wedding guests with Jepsen's hit song "Call Me Maybe" at manager Scooter Braun's nuptials over the weekend.

An excited guest posted the clip to Instagram, writing, "Ah one more! Carly and Justin drop Call Me Maybe and the world explodes. #SYBWedding"

It's true -- the world has exploded!

Braun's married his longtime girlfriend Yael Cohen in a star-studded gathering. Along with clients Beiber and Jepsen, Tom Hanks, Rita Wilson, Sophia Bush, Ed Sheeran and others attended the swanky soiree, held in Whistler.

Moments after exchanging their vows, the Biebs serenaded the newlyweds with "All You Need Is Love" -- a move straight out of Love, Actually

At the fun-filled after party, even Hanks got in on the fun -- dancing to Montel Jordan's "This Is How We Do It" while dressed like a rabbi. All we know is -- we want to do it anyway Tom Hanks tell us to!