Opening up in a new interview, the Scottish actor revealed that the series could look very different from series eight onwards.
WATCH: Shetland series seven trailer reveals Douglas Henshall's final case as Jimmy Perez
"It will be weird knowing they're shooting an eighth series and I'm not there," he told Radio Times, adding: "But I'm not sure what the show is going to be."
Douglas continued: "I hope it works out and I wish them every success, but it isn't going to be the show I was in. They will have to make a whole other show." The details behind the direction in which the series will go are not yet known.
Douglas announced he was stepping down as DI Jimmy Perez last month
The star, who has been a beloved figure in the drama since it began in 2013, will appear in the upcoming seventh series but will not return to the show for series eight, which has been confirmed for 2023.
Douglas previously opened up about leaving the show, writing: "It's been one of the privileges of my career to play Jimmy Perez for almost ten years and to work with so many wonderful people both in front of and behind the camera, and also to spend so much time in Shetland.
"The Isles were so much a part of our show and of Perez himself. I'll miss him and the place. I wish everyone involved much luck with whatever happens next."
Series seven will be his final season on the show
Meanwhile, Douglas is already concentrating on his next venture. According to the 56-year-old's IMDb page, he is currently filming for a new female-led thriller titled Palomino.
The eight-part series centres around a British teacher in Spain called Erin Collantes, who finds herself caught up in a supermarket robbery. After one of the robbers claims to recognise her, her life threatens to unravel.
The logline teases: "In Palomino, a town of secrets, Erin Collantes fights to clear her name and protect her family… But is she really who she claims to be?" Douglas is listed as playing Daniel Long.
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