Watch: When Conor McGregor engaged in a sparring session with Hafthor Bjornsson

Hafthor Bjornsson is famously known as 'The Mountain' from Game of Thrones. Outside of the show, Bjornsson is a professional strongman and was the first person to win the Arnold Strongman Classic, Europe's Strongest Man and World's Strongest Man in the same calendar year.

In 2015, Bjornsson sparred with MMA's biggest star Conor McGregor. 'The Mountain' stands at 6'9" and weighed 400 pounds at the time of his spar with the Irishman.

Check out the video below to watch the sparring session:

The 'Notorious' megastar had the bare-knuckle sparring session with Hafthor Bjornsson before he won the UFC featherweight title against José Aldo at UFC 194.

The Irishman was the dominant fighter during his interaction with Bjornsson. He chased the strongman for the entirety of their session. He hit the Icelandic behemoth with clean straight punches and a splendid jump kick to the body.

" Look how much bigger he is and Conor is playing around with him. Look at the size of this guy and Conor is like slapping him in the stomach. He's getting tired, he's getting tired. Conor is popping him in the stomach with those straight lefts and he knows that dude is getting tired. Look at him, he's backing up. It's funny man and weird to watch, right? ... He gave up!" Joe Rogan said while reacting to the sparring session.

Watch Joe Rogan reacting to the sparring session during an episode of the Joe Rogan Experience below:

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Hafthor Bjornsson believes he could have crushed Conor McGregor in that sparring session

Hafthor Bjornsson spoke to RT Sport MMA a few years back about his sparring session with Conor McGregor. 'The Mountain' said that he treated it as a joke and held himself back because the Irishman had a big fight against Aldo soon after.

Bjornsson also didn't give his all during the session because he believed he had too much power for a man of McGregor's size. The Icelandic strongman believes if he had used all of his strength, he would have crushed the former two-division UFC champ.

Since the sparring session, Hafthor Bjornsson has bagged some combat experience of his own. He's fought in two exhibition boxing bouts to date but is yet to have his hand raised.

He'll he's hoping to change that result when he faces Devon Larratt in a boxing bout this Saturday, September 18.