Dragons are fickle creatures, in Game of Thrones and just about everything else featuring dragons. In A Song of Ice and Fire, dragons obey their masters well enough—as long as the master is truly strong. And they don’t hesitate to turn against each other if their master demands it. The three dragons currently alive in Game of Thrones have never turned against each other, although they are not always totally loyal to Daenerys Targaryen, their master. But Daenerys’ control of her dragons may soon change. In Game of Thrones season 7, it’s very likely that one of the dragons will turn against Daenerys… and that means an incredible battle lies ahead: dragon against dragon.

Game Of Thrones Season 7 Spoilers: Fight Fire With Fire

Once, the Targaryen dynasty was torn apart by dragon-against-dragon warfare. That was the Dance of the Dragons, a cataclysmic Targaryen civil war and probably the largest conflict in Westeros between the Targaryen conquest and Robert’s Rebellion. The war was fought on land, at sea and especially in the skies, where Targaryens aboard dragons would fight with their own kin and lay waste to each other. Dragon warfare proved messy and violent; dragons may be magical, but they’re still animals, and can hurt each other badly. The war ended with the Targaryen dynasty and the dragons themselves decimated; indeed, the dragons went extinct in less than a generation. It weakened the Targaryens forever.

Now, in the third century, the dragons may soon fight again. Daenerys controls all three for now, but when she returns to Westeros, much will change. First, she eventually needs to designate other dragon riders to lead her armies—perhaps a certain Jon Snow?—but that’s not her real worry. The danger comes from Euron Crow’s Eye, the most dire threat to Westeros besides the Night King and Daenerys herself. Euron has an artifact that will transform Daenerys’ invasion: a dragonbinder horn. The ancient Valyrian artifact can supposedly command a dragon to obey. In the books, Victarion Greyjoy has it and will use it to steal a dragon from Daenerys in Meereen. In the show, Euron’s likely to do the same thing in Westeros.

If and when dark magic takes one of Daenerys’s dragons away from her and binds it to the King of the Iron Islands, her war will utterly change. Right now, between the Unsullied, the Dothraki and the dragons, no force in Westeros can possibly resist her. If one of the dragons flips to her enemies, it’s a whole different story. And it could lead to a bloody and violent conflict that will weaken Daenerys and possibly kill one of her precious dragons—just in time for the invasion of cold and death.