The cast of the Juan Antonio Bayona's film already includes Felicity Jones, Liam Neeson and Sigourney Weaver, said The Hollywood Reporter.
'A Monster Calls' is about a young boy who attempts to deal with bullying at the hands of his classmates, and his mother's terminal illness, by escaping into a fantastical world through the guidance of a tree monster.
Kebbel, 32, will allegedly play the boy's father, a man with a history of not being there for his son. Jones is on board as the mother, while Neeson is playing the titular monster. Weaver is playing the boy's no-nonsense grandmother.