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The 13-part series, about the friendship between would-be wizard Merlin and the future King, Prince Arthur, will air in a Saturday evening slot on BBC One from September. It has also secured a run on NBC in the US from early next year.
Hurt, most recently seen in Indiana Jones and the Kingdom of the Crystal Skull, will play the Voice of the Great Dragon, the enigmatic and powerful beast that knows Merlin's true destiny.
Bionic Woman's Michelle Ryan has been cast as wicked sorceress Nimueh, while Heroes star Santiago Cabrera will play Lancelot. Young actor Colin Morgan (pictured) will play the title role, with newcomers Angel Coulby and Katie McGrath starring as Guinevere and Morgana.
Previously-announced cast members include Richard Wilson as Merlin's mentor Gaius and Anthony Head as King Uther Pendragon.
