Here are all the details you need to know about it.
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.
Yep, Rhaegar already had a son named Aegon, with his first wife, Elia Martell (they also had a daughter named Rhaenys).
So why the hell would he name a second son Aegon?!