Dustin Poirier beat Conor McGregor for the second time, at UFC 264, with the American winning by doctor stoppage at the end of the first round as the Irishman seemed to have broken his ankle.
McGregor was on his back for much of the round, after attempting a failed guillotine early in the round, but he managed to get back to his feet at the end of the five minutes.
The former two weight UFC champion missed with a punch just before the time was up for the first round.
As the Irishman's weight went back on his ankle it gave out on him and seemed to break as he fell to the ground clearly in pain.
The referee waved the fight off after McGregor was seen by the doctor, with the Irishman shouting for the fight to be called a doctor's stoppage.
Poirier upset the odds back in January, becoming the first man to knock out McGregor in the UFC, when he caused a second round stoppage on Fight Island.
The pair had been very civil to each other in the build up and immediate aftermath earlier this year, unlike their first fight in 2014, but that changed back ahead of the trilogy fight.
The two men swapped barbs at the pre fight press conference and McGregor even attempted to throw a kick at his rival.
On Sunday, the Irishman looked at his intense best as he headed towards the octagon and, despite being the visiting fighter, had much of the crowd on his side.
Poirier went into the third fight as the favourite and as he entered the cage he was met by his rival attempting to confront him, and had to be stopped by security.
McGregor wasted no time in throwing two spinning kicks in the opening seconds of the fight, before the pair swapped leg kicks, the tactic that won the previous fight for Poirier.
The Notorious, known for his big punching, then had to absorb a couple of great shots from his opponent before wrapping up Poirier in a clinch.
McGregor then tried to wrap up his opponent in a guillotine and took him to the ground but it wasn't in strong enough and the Diamond was able to get free.
With the pair now on the ground it was former interim lightweight champion Poirier who was able to land the bigger shots, even though McGregor did land some elbows and kicks of his own.
Right at the end of the round the Irishman managed to get back to his feet momentarily but injured his ankle in the next exchange and it was over.
It was certainly a shocking ending to the fight, and not the one that many would have been expected or wanted at all.
Whilst Poirier had almost certainly won the first round it doesn't mean the conclusive end to the rivalry that usually goes with a rubber fight.
McGregor had his post fight interview with Joe Rogan whilst still sitting on the octagon floor and called for another fight with his rival.
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"That's a Doctor Stoppage!"
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Conor McGregor heard something he didn't like before the official decision.#UFC264 pic.twitter.com/7UNauiqUWj