Game of Thrones season four is welcoming a new cast member when it returns, and we're sure pop culture buffs will nerd out over this one: Sherlock co-creator and star Mark Gatiss has been cast on the HBO fantasy hit as...

We don't know! Yes, Gatiss' role is being kept top-secret, much like Iwan Rheon's role prior to season three. (He was later revealed to be Ramsey Bolton).

In addition to his time opposite Benedict Cumberbatch on BBC's beloved Sherlock as Holmes' brother Mycroft, Gatiss has written plays and Doctor Who novels and acted in three episodes of the cult classic TV series.

Sherlock, Doctor Who and Game of Thrones? That's like the geek Triple Crown! EW.comfirst reported Gatiss' casting.

沪江娱乐:《权力的游戏》第四季回归时会迎来一个新角色,英剧《神探夏洛克》的剧作者兼演员马克·加蒂斯(在《夏洛克》中饰演夏洛克的哥哥)将会出演HBO的史诗巨作《冰与火之歌:权力的游戏》第四季,至于出演什么角色,我们还不知道。据悉,《权力的游戏》第四季和《神探夏洛克》第三季都将于2014年播出。