Not even book readers would have predicted that Ser Jorah Mormont would get the greyscale in old Valyria, but apparently that's what happened to him at the end of Season 5, Episode 5 of Game of Thrones. Mormont should have seen it coming as well. Vanity Fair pointed out this Easter egg from Season 2.
If only he took Quaithe's prophetic words of warning from Season 2, he probably would have been more cautious. Just in case you forgot, Quaithe is that mysterious masked woman who spoke with Joran in Qarth. Here's what she told him:
And what did Mormont just do this Season? Sail past old Valyria without a damn protection! The King of Friendzone is probably going to turn into someone who looks like The Thing anytime soon, but I hope he gets cured somehow. The writers probably didn't have this in mind, but it's great to see Quaithe's words making sense seasons later. You can check out the Game of Thrones featurette about the stonemen and greyscale below.