Game of Thrones star Hafthor Bjornsson makes steroid admission

Hafthor Bjornsson - before and after. Photo / News Corp Australia

Hafthor Bjornsson has admitted at least part of his stunning transformation from a relatively skinny Icelandic basketball junior into the behemoth that plays The Mountain on Game of Thrones is down to steroid use.

The reigning World's Strongest Man was asked whether he had ever taken steroids in a lengthy interview with ESPN's E:60. "Yes, I have," Bjornsson says. "When you want to be the best, you do whatever it takes."

Asked how often he takes steroids and if he's still doing it, Bjornsson deferred: "Can we just skip those questions?"

The World's Strongest Man competition, which Bjornsson won last year after several near-misses, officially prohibits the use of performance-enhancing drugs.

The E:60 feature charts Bjornsson's journey from Iceland's junior national basketball teams to a professional strongman and Hollywood star.

"My dream was always to become a professional basketball player but that dream didn't go too far," Bjornsson told ESPN.

"I broke my ankle twice. I had to have bad surgeries that ended my career.

"In 2013 the Game of Thrones crew were filming in Iceland and they heard about this massive, muscular, handsome, big young guy.

"At first I got an email. I didn't have any acting experience and getting an email like that out of nowhere from Game of Thrones was like 'nah, that's not true, it's got to be bulls***'.

"So I didn't answer the email. A few days later I got a phone call and it was a man who asked if I wanted to audition for Game of Thrones. I obviously said 'Yes. I don't know what I'm doing but yeah, let's try it'.

"They asked me to pick one guy up, to see if I was strong enough. I picked the man up over my head easily. They were very surprised: 'Woah, OK you're strong'.

"One of the main sword teachers in the show, I fought with him for a little bit with the sword. After about 10 minutes he said 'you're the guy. You're the man we are looking for'."

Bjornsson, who in the past has put his incredible size down to diet and exercise, appears at peace with the risks he takes to maintain his appearance.

"When you are putting yourself through all this. I've always thought about, 'What if I pass away?' It would be very hard to know that I left my family too soon," he said.

"I want to be there for my family. I want to be there for my daughter. But this is my life. This is what I enjoy to do ... People will remember me as the strongest human ever to walk the earth."