What happens when Mariah Carey surprises a bunch of superfans on 'Late Night With Jimmy Fallon'? Cheers, tears and some really great TV, that's what!

Fallon fooled several groups of Mimi's Lambs, saying that he was letting them listen to her new single, 'The Art of Letting Go.' What they didn't know was that Mariah was waiting in the wings to finish the song, live and in person.

The reactions to when she walks out singing are priceless, ranging from utter shock to screaming to bawling. It's a blast to watch, as is Jimmy's obvious delight in pulling off the prank. The talk-show host seriously can't stop smiling throughout.

Carey loved it, too, as she wrote on Facebook yesterday (Nov. 12): "Had so much fun surprising the lambs!!"

It's heartening to see that her album delay and arm injury aren't getting Mimi down.