Now that "Game of Thrones" character Jon Snow has returned to the land of the living, one of the most earth-shaking, series-defining fan theories could be proven true: Jon isn't actually Ned Stark's son; he's the son of the late Prince Rhaegar Targaryen and Lyanna Stark, Ned Stark's sister, according to the theory.
That makes Jon Snow a Targaryen by birth, and makes him the de facto heir to the Iron Throne.
In a series that revolves around the long and bloody battle for that throne -- involving at least six kings, three queens and a war that ravages two continents -- the reveal would change everything we thought we knew about "Game of Thrones."
The theory, dubbed R+L=J, has been circulating on the Internet for years, long before HBO's "Game of Thrones" ever existed and fans were stitching together theories based on the behemothic book series' many subtle clues. Fans have been posting different iterations of the theory on sites like Westeros.org and Reddit for years, piecing it together in a community effort as sharp-eyed readers spotted more clues in the text.
Fans who watched season 1 of the HBO series will remember how Jon was introduced -- as the petulant, bastard son of Ned Stark, the Lord of Winterfell. Jon was raised along with the legitimate Stark children in Winterfell, the ancient castle that serves as House Stark's family seat.
As a bastard, he didn't have any claim to the house, he was a constant thorn in the side of Lady Catelyn Stark -- who saw him as a reminder of her husband's infidelity -- and he couldn't use the Stark name.
Without a future at Winterfell, Jon begs his father for permission to join his uncle, Benjen Stark as a member of the Night's Watch, the militaristic order that guards the Seven Kingdoms from atop The Wall, a 700-foot barrier of ice that separates the realm from the dangerous lands beyond.
Neither character knows it at the time, but it's the last time they'll ever speak. Before Jon departs for The Wall, Ned pulls him aside and says, "The next time we see each other, we'll talk about your mother. I promise."
We all know what happens next. Ned travels to King's Landing to serve as Hand of the King to reigning monarch and close friend, Robert Baratheon. But when Ned uncovers a startling truth about the king's children, he's imprisoned and beheaded in front of a crowd of onlookers in King's Landing.
In the books, while Ned is sitting in a cell beneath the Red Keep, his thoughts turn to Jon, and he laments the fact that he will never get the chance to tell Jon who his mother is. Then Ned remembers a pivotal moment from his youth, when his dying sister -- Lyanna -- asks him to make her a promise.
The previews for episode 3 make it clear we're going to see that scene in a flashback.
Thanks to exposition -- and plenty of reminders -- in the TV show, we already know Prince Rhaegar Targaryen kidnapped Lyanna Stark, setting off Robert's Rebellion, the war that would overthrow the Targaryen dynasty and result in Robert Baratheon being crowned king.
At the end of the war, after Rhaegar is slain by Robert in battle, Ned leads a group of six seasoned fighters to the Tower of Joy in Dorne, where it was believed Rhaegar was keeping Lyanna.
Here's where the theory comes together: Ned does find his sister in the tower, but he finds her in a pool of her own blood, dying of complications from childbirth.
With her dying breaths, Lyanna asks Ned to take her child -- Jon? -- and make a promise never to reveal his parentage to anyone. If King Robert knew Jon was a Targaryen, he'd have the boy killed.
So, Jon Targaryen became Jon Snow. Instead of telling everyone Jon was his sister's child, to keep his promise to his dead sister, Ned tells everyone -- including his own wife and children -- Jon is his bastard son, who he fathered with a commoner while he was off at war.
We're also likely to learn that Prince Rhaegar didn't kidnap Lyanna after all, and that she went with him willingly, wedding him in a secret ceremony attended by only a handful of people. That means Jon Snow is actually Jon Targaryen, paving the way for him to eventually take his seat as the one and true heir to the Iron Throne.
The reveal will likely ripple across the narrative, with serious repercussions for characters like fan favorite Queen Danaerys Targaryen, and the not-so-fan-favorite Lannister family.