Spoilers for Game of Thrones Season 7, Episode 5 ("Eastwatch") lie ahead.
If Game of Thrones ends up secretly being the story of how Gilly became the first female maester at the Citadel, I'd be more than OK with that. After all, she did just casually drop the single most significant piece of information in the show's seven seasons during Sunday night's gripping filler episode ("Eastwatch").
While reading one of High Septon Maynard's old journals — in which he documented everything, even his own bowel movements — she makes an important discovery that has major ramifications for the entire Seven Kingdoms, as well as the show's key players. If only Sam had let her finish!!! Anyway, here's what Gilly was able to decipher from High Septon Maynard's notes before she was so rudely interrupted:
"He issued an annulment for a Prince Rhaegar and remarried him to someone else at the same time in a secret ceremony in Dorne..."
If Prince Rhaegar (pronounced RAY-gar, not RAH-gar as Gilly incorrectly says) was secretly married to a woman in Dorne, then that woman had to be Ned's sister, Lyanna Stark. From what we knew, Ned's younger sister Lyanna was kidnapped by Crown Prince Rhaegar Targaryen and died not long after. Lyanna's abduction triggered Robert's Rebellion, a yearlong war led by her betrothed Robert Baratheon to get her back — and to make the Targaryens pay for what they did.
The bloodshed left House Targaryen all but decimated (or so they thought), and Robert of House Baratheon claimed the Iron Throne for himself, taking Cersei Lannister as his new bride. We know how it all ended, but key pieces of the puzzle were missing.
In the spectacular Season 6 finale ("The Winds of Winter"), Game of Thrones gave us the first piece of the decades-old puzzle: a near-definitive answer to the popular fan theory R+L=J. R and L being Rhaegar Targaryen and Lyanna Stark, and J being Jon Snow.
Thanks to Bran, we know what happened after Ned's fabled fight with legendary knight Ser Arthur Dayne at the Tower of Joy in the Red Mountains of Dorne. In his vision, after Ned stormed the tower, we watched as he approached his sister Lyanna's blood-soaked bed, where she made him promise to protect her newborn son from harm. This is the baby that Ned brought back with him to Winterfell after Robert's Rebellion. Jon Snow wasn't his bastard; he was his nephew. (However, Jon doesn't know this crucial piece of information yet.)
So Jon is the son of Lyanna Stark, and now we know that Rhaegar quietly annulled his marriage to Elia Martell and remarried in Dorne, close to the Tower of Joy where Lyanna and baby Jon were found. While we're going to need Bran to deliver the final piece of the puzzle — expect a vision of Rhaegar's secret marriage before the season's end — it's 99.9 percent clear that Rhaegar married Lyanna Stark. It's also evident that Rhaegar didn't forcefully kidnap Lyanna at all, but rather they ran away together because they were in love.
This means that Jon Snow is not a bastard; he's the legitimate son of Crown Prince Rhaegar Targaryen and Lyanna Stark, a literal product of the dragon prince and the winter rose. As such, he's the rightful heir to the Iron Throne. (Not that he wants that kind of responsibility, or that the Iron Throne will even exist after the Great War.) This all makes his friendly conversation with Gendry, Robert Baratheon's last-living bastard, hella awkward. Remember, it was Robert who delivered that fatal blow to the head of Rhaegar, Jon's actual dad, with his trusty warhammer.
TL;DR — Jon is officially a dragon-taming Targaryen, as Drogon correctly sniffed out during the episode. A dragon doesn't let just anybody touch its face! Drogon knows that there's Targaryen blood coursing through Jon's veins.
Winter may be here, but Jon
Snow Targaryen is about to make it rain fire and blood beyond the Wall. I, for one, can't wait to see the dragon awaken inside the broody King in the North.