Don't get too excited by this thread bump lads, Winds of Winter hasn't been announced
I was just casually browsing through A Wiki of Ice and Fire, as you do, and came across the page of Elaena Targaryen, who I had never really paid any attention to before (although she is mentioned a couple of times in the main series) until I saw her picture and a description of her appearance: "Her hair was a platinum white with a bright golden streak down the middle"
Who else do we know with silver hair with a coloured streak like that? That's right, it's our boy Darkstar!
Coincidence? I think not. There are several theories about Darkstar's true origin, could he be a descendant of Elaena? We know that she married into house Plumm and House Penrose, having children with both, and also had bastards with Alyn Velaryon. Maybe one of these descendants married into house Dayne. We actually know of two of her descendants; Brown Ben Plumm, and the turnkey claiming to be descended from a Targaryen princess, who Jaime almost mistook for Aegon the Conqueror.
Another interesting thing is her dragon egg seems to match the description of Viserion's egg, so her lost egg could be the same one which was given to Daenerys.
Darkstar, the true king of Westeros.
It's possible to argue that Elaena's descendants would be the true claimants to the iron throne, since she and her sisters (who bore no trueborn children) were all passed over for their uncle Viserys II in the succession. So all jokes aside, Darkstar could indeed be the true king of Westeros and become a dragon rider with Viserion as his mount, and that's why he's the most dangerous man in Dorne