Yesterday’s Game of Thrones ended with a devastating, tragic reveal, one that could have implications in future episodes. But, on its own, it closed out one of the bigger mysteries in the GoT universe, explaining why Hodor, a seemingly normal boy in his youth, was only capable of saying his name.

Now, we finally have the answer—and it comes straight from George R.R. Martin.

Warning: Spoilers for season 6 are ahead.

“We had this meeting with George Martin where we’re trying to get as much information as possible out of him, and probably the most shocking revelation he had for us was when he told us the origin of Hodor and how that name came about,” explained David Benioff, one of the show’s writers and executive producers. “I just remember Dan [Weiss] and I looking at each other when he said that and just being like, ‘Holy sh*t.’”

If you caught the episode, you know it was Bran’s meddling in the past that caused poor Hodor to become the simpleton GoT fans have known since season one. Essentially, Bran had possessed the Hodor in the present while still hanging in the past, causing the younger Hodor to seize up as well.

At this moment, we hear Meera shout “Hold the door!” as they’re trying to escape the Weirwood Tree. This causes the young Hodor to repeat her words until finally they meld together into one indistinct phrase. Essentially, Hodor kept repeating Hodor because he kept hearing “Hold the door” when Bran possessed him in the past.

What’s particularly tragic about this reveal is Hodor’s entire life led up to that point, which was to hold the door shut while Meera and Bran ran off into the night. It was a pretty gut-wrenching scene, but one that was important to show off how Bran’s powers can influence the past. When he realizes his potential, who knows what he’ll do with those powers.

Even though HBO’s Game of Thrones has surpassed George R.R. Martin’s books, it’s clear the author still has plenty of influence over the show. I wonder what other big reveals are on the way.

Oh, and for what it’s worth, one die-hard fan of the books essentially guessed Hodor’s fate back in 2014, to which George R.R. Martin coyly responded to.