Ariana Grande Gives Fans Singing 'One Last Time' The Surprise Of Their Lives

What happens when your favorite singer catches you belting out their hit song?

Well, mostly this:

In a montage that “The Tonight Show” shared online late Thursday, pop star Ariana Grande and host Jimmy Fallon creep up on her unsuspecting fans as they sing “One Last Time” ― and their reactions are something else.

Check out the full clip above.