Swedish meatball, Fulbright Scholar and action movie star Dolph Lundgren has told the outlet Aftonbladet he's currently in South Africa shooting for The Witcher. Lundgren doesn't let slip any details about his role, or whether he's filming something for the main Witcher show or one of the upcoming spinoff series, though the speculation is that he may be the lead in a show that will focus on a group called the Rats.
Slightly annoyingly, Lundgren's words are paraphrased rather than a direct quotation. The relevant section in the Aftonbladet article reads: "Now I actually feel better than I have in five years, says Dolph Lundgren and tells us that he is filming a Netflix series in South Africa called The Witcher."
The Rats are a young band of thieves that appear in the Witcher novel Time of Contempt, which the third season of the show (the last to star our boy Henry Cavill) is based on. Thus it's expected the Rats will turn up in season three, do some pilfering and be introduced to the world, before their own spin-off appears.
Collider speculates that Lundgren will play antagonist Leo Bonhart, and it may be the case that he'll be in both the main series and the spinoff. Industry rumours have previously said this spin-off would be filming between April-September this year in South Africa, so the dots do join up. The Bonhart thing is because Lundgren's in his sixties and the Rats are a bunch of teenagers, so it's unlikely he'll be one of those, but Bonhart is a hard-bitten bounty hunter who would suit the man best-known for his portrayal of Ivan Drago.
As for Lundgren more generally, the interview focuses on his recovery from cancer, and mentions he's in the process of being filmed for a documentary about his life. At one stage, the star says a doctor told him he had a few years left, before eventually the right treatment sent it into remission. When asked if he was afraid of dying, Lundgren says "It is clear that I was, I was preparing for my own death. When it's this close it becomes real, but it still didn't feel like the time for it yet. I haven't given up."