A dragon in the hand is worth two in the bush. In Dance With Dragons [spoilers start immediately], Aegon Targaryen arose out of nowhere, a new Targaryen with a much better claim than Daenerys. And he’s already landed in Westeros with the forces of the Golden Company at his back, intent to reclaim the throne that should have been his father Rhaegar’s. Question is… will any of the Great Houses rally to him? More specifically, will House Martell join his cause, or wait for Daenerys to return?

Why House Martell Will Join Aegon, Not Daenerys

For many years, Viserys—and then Daenerys—were the great hope of House Martell, the most serious Targaryen loyalists in the Seven Kingdoms (quite an irony, considering Dorne’s late entry into those kingdoms). For more than 15 years, Doran Martell has held a festering grudge against House Baratheon for the death of his sister Elia in the sack of King’s Landing. Arianne Martell, who is monstrously absent from the television show, was long secretly bethroted to Viserys (very secretly—even she didn’t know). In Dance, her younger brother Quentyn was sent to Meereen to woo Daenerys. Alas, he got burned.

Sooner or later, the Martells will find out about Quentyn’s death by dragonfire… and Daenerys’s rejection of his marriage offer. They won’t understand; they won’t be pleased. It won’t help Daenerys’s odds of winning them to her side. And, of course, she’s still half a world away. She’s probably coming back to Westeros in Winds of Winter—freaking finally—but that’s a long journey.

Aegon Targaryen is already in Westeros, with an army at his back. He may or may not be a real Targaryen, but he’s winning battles and, for now, that’s enough. If he conquers Storm’s End, a citadel that has never fallen, he will gain an immense aura of legitimacy… and he’ll control the Stormlands.

I am a mere fan, not George R. R. Martin, who doesn’t like me. All I can do is speculate, obviously. And behold! I speculate thusly: If Storm’s End falls, the Shield of Dorne will turn into a spear. If Storm’s End falls, the Martells and Dorne will declare for Aegon Targaryen. Arianne may even be pushed to marry him. He is in Westeros. He is successful. He has an army. Daenerys is far away and killed a Martell. And, above all, Aegon is actually a son of Elia of Dorne. If he really is who Varys says he is, he’s Doran’s own grandson [UPDATE: Thanks to the commenters for correcting me—he would be Doran's nephew, not grandson]. Of course the Martells will declare for him over Daenerys.

And when Daenerys does come? Will they join forces? Now that I daren’t even speculate on, but I predict that House Martell shall rise in rebellion against the Iron Throne before Winds of Winter runs its course.