Entertainment Weekly is reporting that Sherlock showrunner, Doctor Who writer, and supremely stuffy Mycroft Holmes Mark Gatiss has been cast in season 4 of Game of Thrones. Unfortunately, the GoT showrunners have not revealed which character he will be playing, but WinterIsComing.net speculates that he will be playing the previously unseen Mace Tyrell, patriarch of the Tyrell family. (A family that, we must say, has been doing a tremendous job of worming their way towards the Iron Throne.)
[More speculation ahead. Mild spoilers.]