"Game of Thrones" cast Pedro Pascal described his fight with Ser Gregor "The Mountain" Clegane as the most challenging stunt he has done, as Twitter fans react to the Red Viper's death.

"'The Viper versus the Mountain,' was one of the most challenging things I've ever done," he told Reddit fans during an AMA session.

As to The Mountain's physique, "Game of Thrones" cast Pedro Pascal only has this to say: "He is the largest person I have ever seen in my life."

The Mountain is played by Icelandic actor Hafthor Julius Bjornsson who stands 6'9" and weighs around 420 pounds of muscle. In contrast, "Game of Thrones" cast Pedro Pascal is around 5'11" and weighs about three times less.

"It felt like I was with a giant. And then put him in the armor, and his sword alone was exactly my height," Pedro Pascal told TVGuide earlier. "It was incredibly intimidating but also really delightful because I think that the character Oberyn really relishes that kind of challenge."

To prepare for the role, the 39-year-old actor trained with renowned Wushu expert, Master Hu, in his studio in Los Angeles. The basics of what he learned in martial arts and how to fight using a spear were used in the movements of the Red Viper.

Meanwhile, Twitter users react to the death of Prince Oberyn, per Fansided.com.

One user wrote: "did anyone else have their heart ripped out because of game of thrones I did."

Peter Budaj added: "Just can't believe that this happens in @GameOfThrones mountain vs viper disappointing."

"Without a doubt that is the most awe struck I've ever been after an episode of Game of Thrones," Danny Archer wrote.

Kyle Bird has some good advice: "Don't get emotionally attached to a Game of Thrones character... theres a damn good chance they will die."