In the days that follow, Samwell Tarly and Gilly arrive at Winterfell. Upon hearing that Bran has found his way home, Sam calls on him and learns the young Stark is now the Three-Eyed Raven. Bran tells Samwell that his new sight has revealed Lyanna Stark as Jon Snow's mother. He also states Jon's father is Prince Rhaegar. Intrigued, Sam reveals that Rhaegar married Lyanna in a secret ceremony. This triggers a vision where Bran sees Rhaegar and Lyanna in a loving relationship, where she bears him a son: Aegon Targaryen aka Jon Snow aka Bran's bastard brother turned cousin.
With this insight, Sam and Bran realize Jon has legitimate blood ties to the Targaryen line. This is a powder keg of a revelation because it suggests that King Robert's Rebellion and the overthrow of the Targaryens occurred based on an elaborate lie. Or to put it plainly, Jon Snow is more than King of the North — he is the rightful heir of the Iron Throne, which means Daenerys Targaryen's tumultuous saga to rule the Seven Kingdoms has been for naught.
Of course, the characters in question are not yet aware of this new wrinkle, but the viewer gets this information just as Jon and Daenerys finally consummate their relationship. And for those of you keeping score on the family tree, this means Jon Snow has just gotten freaky with his aunt. Yes, you read that right. The mother of dragons is having a love affair with her nephew.
