First he beat up his opponent … then Derrick Lewis needed to beat up the toilet!

The Black Beast dropped another gem during his post-fight interview Saturday night … saying, “I gotta take a sh*t” — ON LIVE TV!

35-year-old Lewis had just obliterated #10 ranked heavyweight Aleksei Oleinik in the 2nd round of his main event fight … when the post fight interview with Paul Felder began.

Lewis apparently didn’t realize he was LIVE — because he turned to someone off-camera and revealed he had some junk in his trunk.

The moment was HILARIOUS — but Felder rolled with it like a pro and made sure to hurry up the interview so Lewis could empty his bowels.

Lewis is known for his post-fight antics — remember when he took off his pants in the octagon because he said his balls were hot!?!

Aside from the comedy, Lewis is also a serious run — winning his last 3 fights in very entertaining fashion.

Lewis is currently the #4 ranked heavyweight in the UFC — with a 24-7-1 record.

Enjoy the dump bro, you’ve earned it!