There must be a full moon in Westeros.

The musclebound "Game of Thrones" star Jason Momoa has joined David Hayter's upcoming lycanthrophic thriller "Wolves."

The film stars Lucas Till ("X-Men: First Class") as a young, newly-transformed werewolf who flees home for a mysterious small town called Lupine Ridge, where he comes face-to-face with a host of other supernatural elements. 

Momoa will play the film's main villain role, an alpha male werewolf who controls the town, according to The Hollywood Reporter

"Wolves" marks the directorial debut of Hayter, who co-wrote the screenplays for the first two "X-Men" films and "Watchmen." 

Momoa recently starred in "Conan the Barbarian," and will soon be seen in "Bullet to the Head" alongside Sylvester Stallone and Sung Kang. He also recently wrapped shooting on his own directorial debut, the indie film "Road to Paloma."