WARNING: The following contains spoilers for Game of Thrones.
Game of Thrones had a mixed history with prophecies. While certain destinies that were foretold never came to fruition, others proved to be seemingly set in stone. One of the most important in earlier seasons was the prophecy of Azor Ahai, the Prince Who Was Promised. Various characters were hypothesized to be that Prince, but in the end, none of them turned out to be the mythic figure... Or did they?
A new theory about the finale suggests that the series did, in fact, reveal the identity of the Prince Who Was Promised. And it's none other than Drogon, the last of Daenerys' dragons.
THE PRINCE WHO WAS PROMISED
In the Song of Ice And Fire novel, A Clash of Kings, Melisandre relays the story of Azor Ahai and his prophecized return.
"There will come a day after a long summer when the stars bleed and the cold breath of darkness falls heavy on the world. In this dread hour, a warrior shall draw from the fire a burning sword. And that sword shall be Lightbringer, the Red Sword of Heroes, and he who clasps it shall be Azor Ahai come again, and the darkness shall flee before him."
The prophecy states that "Azor Ahai will be reborn amidst smoke and salt" after a long summer to save the world once more from the Other.
The Other is the book's name for the White Walkers and their leader, The Night King, or Night's King. The long summer is just ending during the early seasons of Game of Thrones, suggesting this it is indeed the time for Azor Ahai to return. Melisandre spends these early seasons believing that Stannis Baratheon is the return of the prophecized hero. However, his army is ends up depleted fighting the forces of Ramsay Bolton and he's eventually killed by Brienne of Tarth in the fifth season of the show.
Melisandre soon discovers a new possible candidate for the title: Jon Snow. She brings him back to life after his murder by the traitorous members of the Night's Watch, implying the Lord of Light has plans for him.
Meanwhile, a priestess in Volantis considered Daenerys as the potential prophecized prince, as the original prophecy was spoken in Valyerian. In that language, "prince" isn't a gender-specific term.
THE DRAGON LORD
The battle against the White Walkers was ultimately ended by Arya Stark, who managed to kill the Night King when he tries to murder her brother, Bran, the Three-Eyed Raven. But, this doesn't necessarily means that Arya was the real Prince Who Was Promised all along. In fact, she only fulfils a few pieces of the prophecy. It's possible that the prophecy itself is a subversion of prophecy tropes in fantasy. In the end, maybe the story of Azor Ahai was just that: a story.
But, a new theory posted on Reddit suggests that the prince was in fact born, and did fight the others. Everyone was just focusing on the wrong species. Drogon was one of the three dragons that hatched during the final moments of the first season. Drogon was more fierce than his brothers Rhaegal and Viserion, and harder to control. He even abandoned Daenerys at one point, only to later return and help fight against the Night King.
Part of the prophecy says the Prince will be born amidst smoke and salt. Drogon was hatched in a funeral pyre. A Woods Witch in the backstory of the books revealed that the new Azor Ahai would be connected to Aerys II of the Targaryen house. This could apply to Jon or Dany, but it could also easily apply to Drogon as, for all intents and purpose, Daenerys was his mother. He even has his own "flaming sword" in the form of his firey breath.
DOES IT HOLD UP?
Drogon wasn't the one to kill the Night King, and his flames (while effective against the Wights and White Walkers) weren't the deciding factor of the Battle of Winterfell. So, at first glance, Drogon couldn't fulfil the prophecy even if he technically does fall in line with certain descriptors.
However, it is possible to interpret the supposed "other" as something else besides the Night King. Drogon changes the world of Westeros forever by razing King's Landing to the ground with his mother. Beyond that, he even destroys the Iron Throne after her death, helping force the remaining leaders to reevaluate how they rule the land.
The specter of ruling has hung over Westeros throughout the entire series, leading to a war that cost thousands their lives over the years. Moving into a republic governing system is at least a step towards democracy. So, in a way, Drogon did save the world from something bad. Though this still feels like a bit of a stretch, probably indicating that the prophecy was far more metaphorical than Melisandre believed it to be.