Justin Bieber Surprises Ariana Grande on Stage, But Just Can't Seem to Remember Her Lyrics—Watch Now!

“Baby” singer has more than a little trouble singing a few lines during his Miami performance

Even the biggest pop stars can have a brain fart!

Justin Bieber delivered quite the surprise Saturday night in Miami when he joined Ariana Grande on her Honeymoon Tour to perform a duet of "Love Me Harder."

As he sang the parts originally performed by The Weeknd, Bieber accidently messed up a few of the lyrics because he didn't remember them completely.

"So I feel bad, I forgot the words Ariana," he told Grande while performing inside the American Airlines arena. "I've been trying to memorize them backstage for like an hour!" 

But don't worry music lovers. Grande wasn't upset at all about the mistake. In fact, the duo continued to perform two songs including Bieber's hit "All That Matters" and "As Long As You Love Me" with Grande taking over the rap verse originally performed by her boyfriend Big Sean. Yes, it's a small music world.

"Thank you @ArianaGrande and thank you Miami," Bieber tweeted. "I missed the stage. See u soon ;)" Grande added, "Thank u Miami babes and thank u @JustinBieber!!!"

As for Frankie Grande's reaction to the special collaboration, let's just say he had tears of joys…literally. In a new YouTube video, the Big Brother alum broke down in tears when listening to the duet live.

"Love you Justin. I love you Ariana," he said while traveling to the Kids' Choice Awards. "Why can't I be in two places at once?!"