Game of Thrones season 7 will kick off a new age of Game of Thrones, with the show becoming a true epic fantasy for the first time. Don’t worry, it will remain a high political drama too, but the war between ice and fire isn’t far off now, and Daenerys Targaryen seems destined to lead the fight—if she can quell the bickering kingdoms in time. She’s got three dragons to fight off an army of the undead, but right now she’s only got one rider. Soon she’ll have two. But, without a critical character from the books, who will be the third? Who is the dragon’s third head in Game of Thrones?

Game of Thrones Season 7 Spoilers: Who Is The Dragon’s Third Head?

Game of Thrones isn’t really a show about destinies and good against evil, or at least it hasn’t been. With the Night King’s coming invasion of Westeros, that’s about to change, and Daenerys Stormborn, bathed in prophecy, is by far the most likely person to lead the defense of humanity (barring a George R. R. Martin-style twist where she suddenly dies or something). The dragons are, of course, the primary weapons in that arsenal. The Dothraki will subdue the Seven Kingdoms, but only the dragons and the Night’s Watch, wielding obsidian blades or Valyrian steel, can stop the white walkers.

Each dragon must have a rider. Daenerys will ride Drogon, as she often does—that’s no question. The second rider isn’t really a mystery either: Jon Snow, who was revealed in the season 6 finale to be the son of Lyanna Stark and Rhaegar Targaryen. He’s Daenerys’s nephew, and if he’s legitimate he actually has a better claim to the Iron Throne than she does. Chances are he’ll end up marrying Daenerys and be the second dragon rider.

But the third is an open question. In the books, you can make a case for Young Griff, the self-proclaimed Aegon Targaryen VI, son of Rhaegar Targaryen and Elia of Dorne. If he is who he says he is, which is very much in doubt, he is the true Targaryen heir to the Iron Throne and could end up being the dragon’s third head. Or he could be a fake, and of little long-term consequence. But no matter: He’s not in the show at all.

So who will ride Viserion or Rhaegal in the show? Fan theories have always pointed to Tyrion, on the off chance that he has Targaryen blood himself (which certainly isn’t impossible). But the dragon rider doesn’t, strictly speaking, have to have Targaryen blood. Anyone of sufficient will can theoretically tame a dragon. And it helps if that person has a dragonbinder horn, which only one person does—Euron Greyjoy, King of the Iron Islands.

In the show, Euron is likely to be a dragonrider, at least for a while. He has the ability and the motivation to steal one of Daenerys’s dragons, and make her invasion of Westeros a lot more complicated and difficult. And that confuses the question of who will ride that dragon against the Night King: Will Euron really steal a dragon? Will one of the dragons die during the ensuing war between Daenerys and Euron? If not, will Daenerys reclaim all her dragons yet again and anoint a third rider, perhaps Tyrion? Or will Euron keep his dragon to the end and ride with Daenerys?

The third dragon rider—the dragon’s third head of prophecy—is one of the biggest mysteries left in Game of Thrones season 7 and 8. But the best candidate right now is probably Euron, and that’s going to be big trouble for everyone.