EXCLUSIVE: BBC One has found another key cast member for its upcoming fantasy series Atlantis. I’m being told that Oliver Walker (Trapped) has joined the cast as a series regular for the show’s 13 episode first season. As with the other members of the main cast, character details are being kept under wraps. It’s unclear why Walker’s name was left off of the casting announcement made by BBC One earlier this week, with one source calling it “hard to explain”. The news comes after TVWise reported earlier this week that both Alice St. Clair (William & Catherine: A Royal Romance) and Ken Bones (The Hour) have landed guest roles on the series, which is sent to begin production next week. Created by Howard Overman (Misfits), Atlantis is set in the city of Atlantis: a mysterious ancient place; a world of bull leaping, of snake haired goddesses and of palaces so vast it was said they were built by giants. It’s into this strange, compelling realm that the young Jason arrives and an amazing adventure begins, bringing to life the vast store of Greek myths and legends. The series is being produced by Little Monster Films & BBC Cymru Wales and stars Mark Addy (Game of Thrones), Juliet Stevenson (White Heat), Sarah Parish (Mistresses), Jemima Rooper (Lost In Austen), Aiysha Hart (Honour), Jack Donnelly (Dancing On The Edge) and Robert Emms (War Horse). Justin Molotnikov (Merlin) is attached to direct.