Warning: There are spoilers ahead if you haven't seen Sunday's episode.

Sunday night's episode of "Game of Thrones" included a battle many fans of the books have been waiting for: The Mountain Vs. The Viper, aka the epic throwdown between Prince Oberyn Martell (Pedro Pascal) and Ser Gregor Clegane (Hafþór Júlíus Björnsson).

The fight's outcome sealed the fate of Tyrion Lannister (Peter Dinklage) who was accused of murdering his nephew King Joffrey earlier this season.

If you're wondering how the gruesome fight was filmed, HBO released a video breaking down how the fight went down.

Björnsson's Mountain character wields a 64-inch sword against Oberyn’s single spear. Since Björnsson is the second-strongest man in the world, Pascal underwent a lot of training beforehand to get in peak physical condition.

“It’s very difficult for the Red Viper to learn the moves because it’s not just a sword, the whole thing’s a bit alien,” said stunt coordinator, Paul Herbert. “We had him do Wushu classes before he came to us. Then, we had a Wushu expert fight with him and learn him about spears to look sharp.”

Wushu is a contact sport based on Chinese martial arts.

"Pedro was very, very good," added Herbert. "He probably had about 40 to 50 moves he would have to learn. So he had three times the amount, four times the amount to learn [than the Mountain.]"

Oberyn's spear consisted of a viper wrapped around the blade with the skin of a python serving as its tassel.

Here are a few GIFs of the two practicing the big fight scene. 


Watch the full video below: 

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SEE ALSO: How the actor who plays the Mountain landed his role on the show