George is at it again, following Benioff and Weiss’s remark of “another day, another knight”. It seems the seventh member of the cast is playing a knight, and he has been in some historical film(s) with the actor who plays Jaime.
The full hint is as follows:
“Ser Seven is another terrific award winning actor. He will be going back to a place he’s been before. This is a guy who once went to the wars with our Jaime, though it’s a good thing that Jaime wasn’t a kingslayer then, or all history might have been changed. And there are mountains in Westeros that he might know, though his character has never seen ‘em.”