It's history repeating itself or at least simultaneously. You would have to really delve into the books to understand the history of everything. It's pretty deep and extensive lore wise.

But ultimately Jon's father Rhaegar became infatuated and obsessed at a young age with this prophecy regarding "The Prince That Was Promised". Azor Ahai is basically this savior that's supposed to come into play with Lightbringer and defeat the Night's King back into a peace treaty or agreement to end the long night.

The prophecy was foretold around Rhaegar's time. He believed it. And basically the prophecy states that the hero would have to come from his bloodline as a Targaryen. Specifically from Aerys and his wife's bloodline. Technically the Children of the Forest are responsible for the Night King's creation and his abilities.

But if you ever get bored this year while waiting on the show to return you should check out the Bran theories. The idea is that Bran is essentially Bran the Builder (who fixed the wall in the past after it was taken down by the Night's King) and that he's also possibly the Night's King himself. The idea and concept is that Bran is somehow effecting the past and present at the same time and history is being repeated or written at the same time in real time. The Three Eyed Raven and Jojen Reed warned him about staying too long in his visions and warging abilities because he could become lost or trapped and never return to his present time. I feel that's the direction this is headed in for the final season. I think Bran is going to warg himself too far gone and he'll get trapped inside the Night King or something to that effect.

It's a very big theory. But I recommend checking it out. I've read all the books and mini series and graphic novels. I love the hell out of it. It has so much detail and little hints and clues that make you want to go back and read it again and again. Right now I am reading the World of Ice & Fire again which really breaks it down for you. There's a lot of answers right there in black and white that GRRM laid out for us to figure out.

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