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"I'm here with Mariah Carey," said Jimmy. "We're going to do this fun thing, we invited a bunch of her superfans to this recording studio so they get an exclusive listen of her new single, The Art of Letting Go."
"They're going to listen to it and we want to get their reactions," he added, "That's what we're telling them."
"They have no idea Mariah's actually going to be singing it in the recording studio, live to them right over there."
"It's a secret," added an excited Mariah, who was dressed in an all-black ensemble and carrying a glittering microphone. "Let's go!"
The groups of fans were already emotional as the track began, many of them holding hands with one another and swaying to the music.
They then burst into loud screams and tears as Mariah, 43, stepped into the room.
"I really had so much fun singing to & surprising my lambs," tweeted Mariah after the show. "Thank you @jimmyfallon for such a great idea!!"
"Pure joy," tweeted Jimmy. "@MariahCarey has some amazing fans!"