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The actor, who plays police sergeant Rob Hollins on the BBC One show, will try his hand behind the camera in the summer.
Speaking on This Morning today (April 24), Walker confirmed: "In July I'm directing for the first time and I'm very, very excited."
Pondering what could happen if the role switch goes wrong, he joked: "It could be the end of everything! It could be the end of the show!"
Walker also made a light-hearted vow not to boss around his co-stars as he directs them - to avoid sparking a revolt.
He laughed: "They'll be stamping their feet, they won't turn up, it'll be chaos!"
Walker's fellow cast members Owen Brenman (Heston Carter) and Matthew Chambers (Daniel Granger) have also directed Doctors episodes in the past year.
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