The actor, whose brother Ryan plays Jason Grimshaw in Coronation Street, joins the show just days after another Corrie sibling finished filming. Grace Kelly, the sister of Coronation Street star Katherine, will appear in an earlier episode in May.
Thomas will play a murderer called Ben when he stars in the serial drama this spring and the episode's storyline will see him reconcile with his mother after being released from a psychiatric institution.
This appearance will be the third time Thomas has starred in Doctors. He made his TV debut on the show in 2002 and appeared as a different character five years later.
"Ben is a rather complicated, intense character and I'm certain Adam will more than rise to the challenge of portraying him," Mike Hobson, the series producer, said. "I'm delighted that we had the opportunity to cast Adam in the role of Ben; he's a wonderful young actor and he undoubtedly has a great future ahead of him."
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