"Game of Thrones" casted its second "mystery role" actor Tuesday, revealing Richard E. Grant as the newest cast member on HBO's hit show.

As has been discussed exhaustively, "Thrones" caught up to George R.R. Martin's A Song of Ice and Fire novels, on which the show is based. So the secrecy in relation to the casting for season six is likely a courtesy as Martin tries to finish Winds of Winter before the show returns.

[Spoilers, but also heavy speculation, to follow]

So that has left so-called book-readers and show-watchers alike to speculate as to who these "mystery role" actors will portray, and whether or not they are characters even Martin has introduced.

Through Entertainment Weekly, HBO confirmed "Thrones" casted Grant, a veteran English actor known for his work on "Downton Abbey," "Girls," "Doctor Who" and more. But first there was Ian McShane, and recent whispers of his filming movements could provide clues to who Grant is playing.

Depending on how many flashbacks "Thrones" is planning, Grant could portray either Howland Reed or Aerys II Targaryen (Daenerys' dead father almost exclusively referred to as "The Mad King"). Reed would be part of the rumored Tower of Joy flashback, but the latter would likely have to be a separate scene entirely (maybe one depicting how Jaime earned his nickname?).

Watchers on the Wall cited unnamed sources who said McShane was filming "a scene" with a particular outlaw band. Watchers previously obtained the casting call for the outlaws, who at least seem similar to the Brotherhood Without Banners (remember Beric and Thoros?).

But more importantly, Watchers learned McShane will not portray Randyll Tarly, Samwell's father and the general of Mace Tyrell's army and will only appear in one episode. If McShane is going to have "minimal screen time" and have an impact on the show, it is possible he will portray Septon Meribald.

Meribald apparently appeared in the first casting call Watchers obtained; he is "salt of the earth" ex-soldier-turned-priest in his "40s or 50s." His role could be part of a major reveal regarding a character assumed to be dead.

Due to its secrecy, "Thrones" has several roles that Grant could theoretically fill and there is nothing to pear down the possibilities, like Watchers did with McShane.