It's Gwendoline Christie!
"There was an amazing, amazing incident one time," the actress — who plays Brienne of Tarth on the show — tells Vulture. "I needed to utilize the little girls' room, and the horse mistress took me over to one of the blue portaloos. I was in there in some strange state of undress, maintaining the armor on top. I was actually simultaneously texting someone, as elegant as I am. And then the whole thing, which was on very muddy ground, started to sort of tip and move.
"There was one horrible moment where I thought, This whole portaloo is going to tip over and I’m going to be trapped with my trousers around my ankles, in full armor, all 900 million kilos of me, on top of the door. They’re going to have to crane me out, and it’s going to be entirely humiliating. Me, in armor, trousers around ankles, phone still in hand. [Laughs.] Luckily, I threw myself back against the back of the portaloo just in time to prevent it from tipping. But it was a lesson: Don’t text and go about your private business. In armor."
It's official. We're in love.