And McGregor makes a notoriously grand splash on to the screen by baring his backside for all to see.

But the Irish icon, 35, admits his mum Margaret has no clue about the shock scene.

He said: “I have my mother coming in for the premiere tomorrow and she has no idea! I’m a bit nervous about it but excited.

“I just done my best. I had a great crew of people with me, a great cast and they were very patient with me.”

McGregor plays the movie’s antagonist, Knox, going up against Gyllenhaal’s UFC star-turned bouncer main character.

And the former two-weight UFC champ shows off some of his trademark striking skills in the movie.

But his three sons Conor Jr, six, Rian, two, baby boy Mac and daughter Croia, five, will have a life-time ban on watching their daddy on the big screen.

The doting dad said: “Obviously, they can’t watch and never will, to be honest. I’m nervous about my mother seeing it.”

McGregor – who has not fought since July 2021 – revealed he was putting in exhausting 18 hour days on set.

And he revealed Gyllenhaal’s brave stuntmen were on the receiving end of some of McGregor’s iconic KO shots.

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McGregor said: “He had a multitude of stunt guys and they got f***ed up, they actually got f***ed up and they wanted me to f*** them up.

“There was like spinning back kicks to the ribs and the director was like, ‘No go again!’

“I was like, the guy’s on the f***ing floor here! But it was a great experience.”

5McGregor plays the main antagonist in the movieCredit: @TheNotoriousMMA5It marks the UFC legend’s Hollywood debutCredit: @TheNotoriousMMA5McGregor in a behind-the-scenes snap