The Biebs appears on Puerto Rican singer Luis Fonsi and reggaetón star Daddy Yankee's "Despacito."
The song is sung in Spanish (the title means slowly in Spanish), and it recently hit number one on Billboard's Hot 100.
Naturally, since it's such a hot summer jam, fans have been wanting Bieber to perform it.
The trouble is, he doesn't know the lyrics.
At the recent Summerburst Festival 2017 held in Stockholm, Sweden, Bieber told the crowd he couldn't sing the song.
"I can't do 'Despacito,'" Bieber said on stage. "I don't even know it."