Game of Thrones on HBO
'Game of Thrones' on HBOFacebook/ Game of Thrones

Sunday's episode could be the beginning of the end for Ser Jorah, who ended up contracting greyscale after fighting with the stone men.

But what is greyscale? According to "Game of Thrones" wiki, it is a deadly and often fatal disease that leaves the skin stiff and cracking. People who have once contracted greyscale will be immune from it in future. But the damages caused by the disease will never heal, and people with greyscale will be scarred for life.

One popular "Game of Thrones" character who has greyscale is Princess Shireen Baratheon, who caught the disease as an infant. She survived the disease, but it has left her face disfigured.

Actor Iain Glen, whose character Ser Jorah is the latest victim, opened up to Entertainment Weekly about finding out about the awful twist while reading the script.

 "I thought, 'Uh-oh, here comes trouble,'" Glen said. "Then you start reaching out for what this means, and [showrunners Dan Weiss and David Benioff] are playing their cards very close to their vest on this one."

 "You wouldn't think good," he said. "But in this story, people have died from it and they have been saved from it. So who knows? It's a slow burn, greyscale, and there are ways to intervene."

As for what's next for his character Ser Jorah, Glen did not reveal much, but noted that his character will be involved in a major action scene later in the season.

"I've had bits and pieces of fighting through the course of the seasons," he said. "I had the one-to-one with the Dothraki bloodrider, and then there was the sequence fighting to get into the city of Meereen. But this season will be the most substantial fighting I've had."

"Game of Thrones" airs Sundays on HBO. There are five more episodes left in the season.