Alexander Skarsgård on facing the Mountain from Game of Thrones in The Northman : 'I was intimidated'

Alexander Skarsgård has faced the Mountain from Game of Thrones and lived to tell the tale.

The plot of The Northman, the new Viking revenge film from The Witch director Robert Eggers, sees Prince Amleth (Skarsgård) fleeing his homeland after witnessing his uncle Fjölnir (Claes Bang) murder his father (Ethan Hawke) and capture his mother (Nicole Kidman). Amleth returns years later as a fully grown berserker to avenge his family.

Part of this bloody odyssey means he must pass himself off as a slave on Fjölnir's land, which puts him in a physical tussle with a fellow slave, played by Hafþór Björnsson, the hulking Icelandic strongman behind Gregor Clegane/the Mountain from HBO's Game of Thrones.

"He came out to set when we were shooting a scene, the first time you meet Amleth. Hafþór wasn't, obviously, working that day, but he came to set just to say hi to everyone. And, yes, I was intimidated," Skarsgård tells EW of meeting his 6-foot-9 cast mate. "Shaking Hafþór's hand — I'm 6' 4'' — I was like [Skarsgård strains his head to look up], 'Hi, sir. It's a pleasure.' His hand just dwarfed mine."

Aiden Monaghan/Focus Features; HBO 'The Northman' sees Alexander Skarsgård facing off against 'Game of Thrones' actor Hafþór Björnsson.

Eggers confirms that, much like the Mountain, Björnsson was a man of few words: "We'd do a take, and he would be like, 'Are you happy with Hafþór?' I'm like, 'Yes. Yes, it's great.' "

Skarsgård promises Björnsson is a gentle giant, but he recalls the challenges of pulling off such a physical scene with one of the world's most famous heavyweights. "He tried to go easy on me, but he still has to tap me lightly and I just went flying," the actor says with a laugh. "I was definitely quite sore after that week of filming. You do not want to fight the strongest man on the planet."

The entirety of The Northman, which maintains a fast pace and wild energy, was both physically and mentally challenging for everyone involved, according to Skarsgård. He points to a scene that takes place early on in the movie — a band of berserkers pillaging. Amleth roars through the village with blood and dirt smeared on his body as dozens of animals and extras go wild in the background through an extended take.

"It's an undertaking that is almost borderline insane, but I also really thrive on that, the madness of that and the possibility of shooting a big action scene like that in a way that could potentially feel more immersive than all the other action movies," he says.

The Northman opens in theaters this April 22.

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