Nicholas Hoult and Thandie Newton have also joined the cast of Dolan's first English-language film, which stars Chastain as a villainous gossip columnist, said The Hollywood Reporter.
"Game of Throne" actor Kit Harington stars as an American TV star in his late 20s and his correspondence with a young actor-to-be living with his mother in England.
Their lives take a dramatic turn when the existence of their pen-pal relationship is publicly exposed by a gossip columnist. A decade later, the younger actor revisits the events over the course of an interview.