Aegon (Jon) and Daenerys are the last surviving members of House Targaryen that ruled Westeros for almost 300 years. The Targaryens were once a mighty house -- especially when they had dragons. However powerful the Targaryens seemed to be, the truth is that they were a fairly minor House in Valyrian Freehold, the mighty empire that ruled half the world for thousands of years. Then, the Doom happened, bringing with it the destruction of palaces, temples, towns, and, most importantly, the death of almost all Valyrian Dragonlords (as well as their dragons).

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The Targaryens would have succumbed to the same fate if it wasn't for Daenys the Dreamer who foresaw the Doom twelve years before it happened. It was because of her dream that the Targaryens escaped Valyria in time.

They settled on the island of Dragonstone, from where they would later conquer Westeros. And the rest, as we all know, is history.

The Doom, on the other hand, remains a mystery. What/who caused it? There are a couple of theories. Some say it was the Faceless Men [VIDEO], some say the Children of the Forest, others say both. A couple of days ago, another theory emerged, claiming it was someone else.

The Doom of Valyria

The Doom of Valyria involved fire magic, usually associated with dragons (as opposed to ice magic that's connected to the far North, The Lands of Always Winter, and of course, the White Walkers). YouTube channel Alt Shift X points out that Valyria and the Lands of Always Winter seem to be the center points of ice and fire. After all, both of these places had their disasters.

The Lands of Always Winter brought the Long Night [VIDEO] and Valyria had the Doom. That, according to Alt Shift X, affected the world's magic.

The new theory

Alt Shift X also put together a pretty complex theory explaining what caused the Doom. As with most "Game of Thrones" theories, this one begins with a prophecy. "The World of Ice and Fire" states that the Freehold's sorcerers foretold that the gold of Casterly Rock would destroy them.

Casterly Rock is, of course, the ancient seat of House Lannister, the richest family in all of Westeros. What Lannisters didn't have, however, was the Valyrian Steel sword. They bought a Valyrian Steel sword, costing them a large sum of gold. It is not known who sold this Valyrian Steel sword (Brightroar) to the Lannisters but if this gold went to Valyria it could've fulfilled the prophecy of Valyria's destruction.

"The World of Ice and Fire" also says that the great families of Valyria were involved in constant conflict which might have led to the assassinations of sorcerers whose spells held back the Fourteen Flames (the fiery mountains of Valyria).

According to Alt Shift X, it was the Targaryens who sold Brightroar to the Lannisters and then used that gold to pay the Faceless Men to carry out these assassinations, which led to the Doom of Valyria. If this theory is true, that would mean that Daenerys and Jon's family took power through this genocidal betrayal, which might explain why they were nearly wiped out during Robert's Rebellion.

Watch Alt Shift X's video below for more details: