I just watched the Doctor Who episode 'Eaters of Light' and in the preview of the next episode it showed Missy dancing with the Doctor and John Simm smirking that classics evil smile. Is John Simm returning to replace Michelle Gomez as the new/old Master?
This was confirmed by the BBC all the way back in April. From this article:
"I can confirm that it's true, thanks to the power of time travel I'm back," Simm said. "It's always a pleasure to work with this great team of people and I can't wait for you all to see what The Master gets up to in the next series."