Although Jon Snow still knows nothing, Game Of Thrones fans know more than perhaps they want to, thanks to the Season 7 finale. Spoilers follow. With the powers of Sam and Bran combined, the two of them were unable to untangle Jon Snow's complicated heritage in "The Dragon And The Wolf." Bran uses his raven power to learn that his former half-brother is not Jon Snow or Jon Sand, but that Jon is really Aegon Targaryen on Game Of Thrones — the legitimate son of Rhaegar Targaryen and Lyanna Stark. While most fans had previously figured out R + L = J, the fact that it's actually R + L = A is a surprise. Beyond this bombshell being revealed as Jon has sex with his Aunt Daenerys, the truth about Jon's real name on Game Of Thrones may mean even more trouble for these Targaryen relatives.
When Bran sees his Aunt Lyanna tell his father Ned in a past vision that her son's name is Aegon Targaryen, it should have rung a dragon-sized bell for Game Of Thrones fans. It was a popular family name for House Targaryen before they were defeated in Robert's Rebellion. The last Aegon to sit on the Iron Throne was Aegon V — or "Egg," as the maester of Castle Black (and Aegon V's brother) Maester Aemon called him. Since Maester Aemon spoke of Egg, Sam knows the importance of Jon's name right away since Aegon V was the grandfather of the Mad King.
But everyone in Westeros should know the significance of the name Aegon Targaryen since the first Aegon was Aegon the Conquerer, who originally united all Seven Kingdoms for his family. But besides it being extremely bold for Lyanna to name her son Aegon (Vanity Fair writer Joanna Robinson likened it to naming an American kid George Washington), it's also a bit bizarre. That's because Rhaegar already had a son named Aegon with Elia Martell. When Lyanna had Jon, Rhaegar's first Aegon son had already been murdered by the Mountain during the Sack of King's Landing. Rhaegar was also dead, but it's still super weird to name your son after your husband's dead first son with another woman.
However, choosing the name Aegon for Jon wasn't because Lyanna wasn't able to think of anything better. As Vanity Fair noted, in the books, Rhaegar had wanted three children — to go along with the three-headed dragon theory — and he thought that his first Aegon was "the prince that was promised, and his is the song of ice and fire." Elia was unable to give Rhaegar another child, but Lyanna was. And with Bran's new information about Jon's true name, Jon's fate of being the prince that was promised seems officially solidified since Rhaegar's third child, Prince Aegon Targaryen, is the perfect combo of ice and fire.
Now, Bran and Sam just need to let Jon in on his family's secret.