One of the lead stars in HBO's "Game of Thrones" epic battle between The Viper and The Mountain, Hafnor Julius Bjornsson made a lot of buzz on the latest episode of the network's fantasy series. Best known for his role as the freakishly large knight Gregor Clegane. 25-year-old Icelandic athlete is Cersei's champion to hang Tyrion for the crime he did not commit.

In an interview posted on New York Post, the actor revealed that he has to limit his strength when it comes to fighting with Oberyn Martell played by Chilean actor Perdo Pascal. GOT season 4, episode 8 ended in a bloody finale when The Mountain crushed the head of The Viper which sealed Tyrion's fate for the upcoming episode.

Feared for his size, cruelty and prowess in battle, The Mountain wears the thickest plate armor in Seven Kingdoms and carries an extremely thick oaken shield. Known as the brother of The Hound, Sandor Clegane, Gregor is the one responsible of The Hound's facial scars and based on rumours he even killed his own father, sister and two wives.

Here are the five amazing facts about Hafnor Julius Bjornsson, the feared 'Mountain' in "Game of Thrones:"

1. Before the Icelandic actor landed the famous role, Conan Stevens played the Gregor Clegane in the show's season 1 and Ian Whyte in Season 2. During his audition to the role, GOT showrunners were quite surprised with how fast he could move despite his massive size.

"I am really fast, not boasting; it is a fact," he said in an interview with the publication. "Then they asked me to lift a man, grabbing under his armpits and lifting him over my head. They said he looked like a baby in my hands. Well, at least I got the part. I mean, who would not love to be in "Game of Thrones" as the Mountain?"

2. To learn how to use a sword during the duel, Bjornsson had an intense training with the sword master, C.C. Smiff. They trained from early morning until evening for weeks just to prepare for GOT's highly-anticipated fight.

3. Although single, he has a 5-year-old daughter.

4. When asked if people are scared of him because of his size, the actor said, "I am no monster, just a nice guy."

5. He got his towering height of 6'9" at the age of 15-16-years-old and maintains a high-carbo diet to keep his imposing built.

"Game of Thrones' season 5 returns to HBO on Sunday, June 8.