The Season 7 finale of Game of Thrones saw many of Westeros' major players finally meeting face-to-face, and that ending left viewers with plenty of hype for the eighth and final season of the HBO series. It's the long-awaited reveal of Rhaegar and Lyanna's son's name that has readers diving back into George R.R. Martin's novels however, because everyone's looking for clues about Aegon Targaryen from the Game of Thrones books.
Spoiler warning: Major spoilers about the Game of Thrones Season 7 finale to follow. If you don't want the episode's biggest reveal spoiled for you, I suggest reading something else.
In the seventh episode of Game of Thrones Season 7, titled "The Dragon and the Wolf," Daenerys Targaryen and her closest allies finally make it to King's Landing, armed with a captive White Walker that they hope will convince Cersei Lannister to call a winter-long truce. Afterward, as Jon Snow sails north with Daenerys, the action cuts to show Samwell Tarly making his way to Winterfell, where he finally swaps information with the Three-Eyed Raven, formerly known as Bran Stark.
Because he's now the Three-Eyed Raven, Bran can see pretty much anything that has ever happened, or that is happening right now. Bran knows that Jon was not his father's bastard son, but the child of his late aunt, Lyanna Stark, and Prince Rhaegar Targaryen, the Mad King's eldest son and Daenerys' older brother. But when he tells Sam that Jon's name should really be "Jon Sand" — because he was born in Dorne, and Dornish bastards are called Sand — we find out what Bran hasn't seen yet.
As a Maester-in-training, Sam had access to a lot of ancient lore, including a successful remedy for Greyscale. Thanks to Gilly, Sam has discovered a passage in Maester Maynard's private journal detailing how Prince Rhaegar had his marriage to Elia Martell annulled so that he could marry Lyanna in Dorne. The old Maester even recorded the name of the newlyweds' child: Aegon Targaryen.
Here's what we know about Aegon Targaryen from the Game of Thrones books.