We know it's tough to come to terms with, but if you don't believe us just check out this video of the Biebs throwing punches after church.

You know he looks fast. Admit it.

Before you act too shocked, remember Justin used to train quite a bit with his (ex?) friend Floyd Mayweather, who once told TMZ Sports that if JB wanted to, he could seriously be a boxing star.

Bieber put on his little display earlier this week after a Hillsong Church service ... and his quick hands look up-to-date to us.

Watch how you talk to Selena.