The 11th Doctor has been added to the cast of Episode IX in what is described as a "key role.” According to Variety:
Sources tell Variety that “The Crown” star Matt Smith is joining “Star Wars: Episode IX,” which is currently in production in the U.K. It’s unknown at this time whether the “Doctor Who” alum will be on the side of the rebels or the evil empire.
Now it should be noted that the headline mentions a "key role", but the body of the article does not. Headlines are often suggested by the article's writer, but the final decision is made by the copy editor on up, so that might explain the disconnect.
Finally, the shape of Matt Smith's head has a bit of a Muun appearance. But I wouldn't presume to play at a guess at what that means.