Ariana Grande surprises superfans while they think they're filming a fan video covering her songs - not realizing she is in the other room listening. Subscribe NOW to The Tonight Show Starring Jimmy Fallon: http://bit.ly/1nwT1aN Watch The Tonight Show Starring Jimmy Fallon Weeknights 11:35/10:35c Get more Jimmy Fallon: Follow Jimmy: http://Twitter.com/JimmyFallon Like Jimmy: https://Facebook.com/JimmyFallon Get more The Tonight Show Starring Jimmy Fallon: Follow The Tonight Show: http://Twitter.com/FallonTonight Like The Tonight Show: https://Facebook.com/FallonTonight The Tonight Show Tumblr: http://fallontonight.tumblr.com/ Get more NBC: NBC YouTube: http://bit.ly/1dM1qBH Like NBC: http://Facebook.com/NBC Follow NBC: http://Twitter.com/NBC NBC Tumblr: http://nbctv.tumblr.com/ NBC Google+: https://plus.google.com/+NBC/posts The Tonight Show Starring Jimmy Fallon features hilarious highlights from the show including: comedy sketches, music parodies, celebrity interviews, ridiculous games, and, of course, Jimmy's Thank You Notes and hashtags! You'll also find behind the scenes videos and other great web exclusives. Ariana Grande Surprises Fans While They Sing "One Last Time" http://www.youtube.com/fallontonight #ArianaGrande #FallonTonight #JimmyFallon