The Biebs showed up to duet with Ariana Grande, then promptly forgot the words to her song.

Justin Bieber made a surprise appearance at Ariana Grande's show in Miami over the weekend, and he gave Ariana a bonus surprise of forgetting the lyrics to the song he was dueting on, "Love Me Harder." But Bieber followed Bieber rule #1: If you don't know what to say, just replace it with swag. (It's similar to Bieber rule #2: If you don't know how to look when getting your mugshot taken, smile.) Instead of singing the latter half of the song, J Biebs simply strutted around the stage and touched the hands of screaming tweens ("scweens").

He did immediately and profusely apologize after the song (bump to 2:10 in the video to see that part), and he apologized again on Instagram as well:

Sources: US Weekly