The news came during the GOT Comic Con panel, which featured Kit Harington, Maisie Williams, Sophie Turner, Gwendoline Christie, Natalie Dormer, John Bradley, Nikolaj Coster-Waldau, Rory McCann, Pedro Pascal and Rose Leslie, along with producers David Benioff and D B Weiss and writer George RR Martin, reported Contactmusic.
Among the new faces joining the show will be Alexander Siddig, who plays Doran Martell, the rule of Dorne and the older brother of the slain Oberyn.
Elsewhere, the Oscar-nominated New Zealand actress Keisha Castle-Hughes - best known for Whale Rider - will play Obara Sand, one of Pirnce Oberyn's illegitimate daughters who is seeking revenge for her father's murder at the hands of the Mountain, in season four.
The 'London' star DeObia Operei will play Areo Hotah, the loyal protector of Doran Martell.
Probably the most recognised among the new inclusions is Jonathan Pryce - who will play High Sparrow, a religious figure. Pryce is a hugely successful actor, best known for playing Bond villain Elliot Carver in 'Tomorrow Never Dies'.
Others joining 'Game of Thrones' include Nell Tiger Free, Jessica Henwick and Enzo Cilenti.