Early on in Game of Thrones, Jon Snow asks Samwell Tarly why his surname is Snow. “Because,” his loyal Wall companion slowly responds, “you’re a bastard from the North.” Jon Snow’s real name isn’t Jon Snow — it’s… well, that hasn’t been officially established yet. The closest we got to an answer came in the season six finale during the Tower of Joy flashback, where it’s confirmed that Rhaegar Targaryen (R) and Lyanna Stark (L) are Jon’s parents (J). Before she dies, Lyanna whispers something to her brother Ned, and although HBO intentionally didn’t provide closed captioning for the scene, a close, lip-reading inspection has some viewers believing “what she says is Jaehaerys.”
Who is Jaehaerys? As we wrote at the time:
Jaehaerys I Targaryen was the king of the Seven Kingdoms — the fourth Targaryen to hold such a title — approximately 200 years before the start of the series. He was dubbed “The Conciliator” or “The Wise.” A century and a half later, Jaehaerys II Targaryen became the 16th Targaryen to sit on the Iron Throne, and almost the last. That dishonor went to his son, Aerys II, better known as the Mad King, or Daenerys’ father. (Via)
Ned couldn’t name Lyanna’s son “Jaehaerys,” though, because that would give away his Targaryen bloodline, so he went with “Jon,” possibly in honor of his friend and Hand of the King predecessor, Jon Arryn. Or so the thinking goes. Again, nothing’s been established in the books or on the show, but the theory may have been confirmed in, all of places, Empire magazine.