People Magazine reports that Justin Bieber sent Ariana Grande fans into a tizzy when he appeared onstage in a surprise performance during her Miami, Florida concert – in spite of a lyrical flub during their duet.

Grande, who headlined the American Airlines arena on Saturday for her Honeymoon Tour, began the words to her newest single “Love Me Harder,” before Bieber came out to sing alongside her.

The pint-size pop prince took the parts of the song originally performed by new pop favorites The Weeknd, but he apparently didn’t quite have all the lyrics down. “So I feel bad, I forgot the words, Ariana,” he apologized to Grande after the song ended. “I’ve been trying to memorize them backstage for like an hour!”

Grande graciously reassured him, insisting that “nobody heard,” and the two continued their duet on Bieber’s own hit tune “All That Matters.” The singers, both 21, also took on “As Long As You Love Me,” with Grande handling the rap verse originally performed by her boyfriend, hip-hop artist Big Sean.

Later that night, Bieber shared a photo of the two on stage, chuckling over his minor lyrical mishap.

“Had fun with u Ariana, even tho I forgot all the words haha,” he wrote.

The “Beauty and a Beat” singer also had tour rumors buzzing when he tweeted after the show “Thank you @ArianaGrande and thank you Miami. I missed the stage. See u soon ;).” Soon after, he wrote “Great night. Loved being back on stage. Miami I’m not done yet…”

Bieber has not graced his fans with a concert tour since his Believe world tour, which ran in 2012 and 2013.