Ashton-Griffiths - who will soon be seen as Alfred Hitchcock in the Nicole Kidman-headlined Grace Kelly biopic Grace of Monaco - becomes the fourth person to join Game of Thrones ahead of its fourth season, with Pedro Pascal (Graceland) set to portray Oberyn Martell, Indira Varma (Rome) cast as his mistress Ellaria Sand, and Mark Gatiss (Sherlock) signing on for an as-yet-unrevealed role.
Filming on season four of Game of Thrones is now underway with the show set to return to TV screens early next year.