Disguised Justin Bieber surprises fans on ‘Friends’ set, sings ‘Smelly Cat’

Justin Bieber has had a long of hit songs in his time, but instead of singing one from his repertoire, he recently donned a costume and convinced unsuspecting “Friends” fans to sing along to “Smelly Cat” as they toured the iconic show’s set.

For those not up to snuff on their “Friends” trivia, “Smelly Cat” was character Phoebe’s most popular and memorable song from the show.

Bieber appeared on a recent episode of the “Ellen DeGeneres Show” that was guest-hosted by fellow performer Demi Lovato. In a pre-taped segment, he wore a WB Studios tour guide uniform and fake facial hair to take photos of unsuspecting fans.

In one especially awkward moment, he fluffed the pillows behind two men sitting on the classic orange couch in Central Perk. In another, he asked a couple posing for a photo to kiss.

Though he seemed to reveal his identity to most of the people he messed with, one couple apparently never figured out it was him! They sat in the audience of the "Ellen" show taping and learned they’d been pranked.

“Are you serious? You had no idea until right now?” Bieber laughed. “Let me ask you this: Did you think the guy was weird or did you think he was cool?”

“I thought he was both,” the gentleman from the audience replied. “Great energy.”

This isn't the first time the show has pranked unsuspecting fans at the nearby "Friends" set at the Warner Bros. Studio lot in Burbank, California.

Earlier this year, Jennifer Aniston — who famously played Rachel on the show — scared fans by popping out from behind the couch.