A former UFC fighter, who is now a police officer, fought an ex-con in a bare knuckle fight and it ended in brutal fashion.

Bare Knuckle Fighting Championship (BKFC) pitted Jimmie Rivera, who is now a full-time police officer, against Brandon Meyer, who has served 12 years in prison, in the co-main event.

Given the matchmaking, it was billed as cop vs criminal at BKFC 95.

Rivera had an extensive MMA career, having fought for Bellator, WSOF and the UFC. He won four fights under the Bellator banner before joining the UFC in 2015, where he had 11 fights inside the famed Octagon.

The New Jersey native won five UFC fights in a row, beating the likes of Pedro Munhoz, Urijah Faber and Thomas Almeida, emerging as a top bantamweight contender in the process. He also fought former UFC champions Aljamain Sterling and Petr Yan before taking off the gloves to embark on a bare knuckle career.

Cop vs Ex-Con Bare Knuckle Fight

The bare knuckle fight between the cop and former prisoner was played up in the build-up, with Rivera hyping up the clash in his final pre-fight interview.

"He gets to beat me up and not get arrested for it, so it’s a win-win," he said.

Well, Rivera vs Meyer lived up to its billing and produced a jaw-dropping finish in the fourth round.

The 37-year-old had Meyer backed up against the ropes and unloaded several punches before landing an explosive left hook that detonated flush on his foe's chin.

The blow immediately slept Meyer, who crumbled to the canvas, with the referee waving off the contest.

Meyer eventually regained consciousness and could be seen attended to by doctors inside the ring.

Jimmie Rivera Explains Why He Apologised to His Opponent After KO Win

Rivera collected his fourth win in bare knuckle, moving to now 4-2-1. He's on a two-fight winning streak following his victory over Timmy Mason last year.

Speaking after his latest BKFC win, the 37-year-old explained why he apologised to Meyer and his team, revealing his opponent had his kids in his corner.

"It's unbelievable," he said about his win on home soil. "Thank you, New Jersey, my friends, my family, everybody that's a fan coming out, supporting me at the Prudential Center. This is a huge arena, and it's f**king packed out."

Rivera continued: "I feel really bad because his kids were in his corner, and the shot that I landed was a shot. You know, so I apologised to them and said sorry, but I was looking for that one shot, taking my time, and surprisingly, he wasn't engaging as much. So I was really looking for him to engage more. I was not looking to run into things."