In the Season 7 finale, Game of Thrones once and for all confirmed a decades-old fan theory, revealing that Rhaegar and Lyanna Stark were married, and that their son, Jon Snow, is actually a legitimate Targaryen named Aegon.
While the truth about Jon's parents came as no surprise, his real name left a lot of fans confused.
Yep, Rhaegar already had a son named Aegon, with his first wife, Elia Martell (they also had a daughter named Rhaenys).
It makes sense that, if Rhaegar wanted his successor to be named "Aegon", he would use the name for his child with Lyanna, his legitimate heir.
But why would he be so set on the name Aegon? Probably because it's the most powerful name in the Targaryen family, dating back to Aegon the Conqueror.
Aegon the Conqueror was the Targaryen who – as his title suggests – conquered Westeros and unified the Seven Kingdoms into one, establishing the Targaryen dynasty that would rule until Robert's Rebellion.
There were several kings called Aegon after Aegon the Conqueror – most recently, Aegon V, a.k.a. Egg, the brother of Maester Aemon and a main character in George R. R. Martin's Tales of Dunk and Egg series.
But there's likely more to it than Rhaegar simply wanting a powerful name for his heir – there's a good chance he believed Jon/Aegon would be the prince that was promised, a.k.a. the person who would save the world from the coming Long Night.
In the books, Daenerys' vision in the House of the Undying is quite different than it appeared in the show in Season 2. She actually has a vision of Rhaegar, with what many fans have always assumed was Elia and their son Aegon. But now it seems it's actually a reference to Lyanna and baby Jon.
Of course, Rhaegar annulling his marriage to Elia, delegitimising his first two children, and naming a second son Aegon, makes him seem like a massive jerk. It'll be interesting to see if his character and feelings – not to mention Lyanna and Elia's – will be explored further in Season 8, as Jon reckons with the truth about his parents.
There's also the chance that, since Rhaegar was dead before Jon's birth, it was Lyanna who chose the name Aegon. Perhaps she wanted to honour Jon's half-brother, who was also already dead by that stage.
To me, it seems likely that Rhaegar chose the name Aegon for Jon, and it's connected with Dany's vision and the prince that was promised prophecy.
For now, one thing is certain: his name may be Aegon Targaryen, but he'll always be Jon Snow.