Aegon is the youngest and only living child of Rhaegar Targaryen and his wife Elia Martell. At the night he was conceived a comet fell above King's Landing. He was born a year earlier than his aunt, Daenerys Targaryen. Some people believe that he is the prophesied "The Prince Who Was Promised".
Aboard the Shy Maid a young man claiming to be Aegon explains his apparent survival to Tyrion Lannister. According to his account, the infant killed during the Sack of King's Landing was a tanner's infant son born at the Pisswater Bend, a street of King's Landing.
The child's mother had died at birth. The tanner sold his boy to Varys for a jug of Arbor gold wine, since he already had other sons, but had never tasted Arbor gold. Varys then arranged the swap between the two infants. Elia received the tanner's son (whom Tyrion dubs the pisswater prince), while Varys and Jaehaerys Targaryen - Aegon's great-uncle - took custody of the real Prince Aegon.
Tyrion Lannister deduces the rest of the story. Once the impostor infant was "safely dead", Varys and Jaehaerys smuggled the genuine Aegon Targaryen across the narrow sea. They first entrusted the boy to Illyrio Mopatis and eventually found an adoptive father for Aegon in the person of exiled Lord Jon Connington. Aegon does not comment on Tyrion's deductions.
Jorah Mormont captures Aegon and Tyrion intending to take them to Daenerys. They are taken to one of the fighting pits, and when Jorah learns that Daenerys is present for the opening of the games, he takes a sword and enters the arena, knocking out the other fighters while disguised with a helmet. Jorah approaches Daenerys and removes his helmet to reveal his identity, but Daenerys, who still hasn't forgiven him, orders Jorah to be taken away. Jorah informs her that he has brought her gifts, and Tyrion and Aegon reveal themselves, meeting Daenerys face-to-face at last.
Aegon continues to hide his identity from Daenerys. Instead, he introduces himself simply as "The Young Griff". Daenerys remains suspicious towards Aegon.
Aegon fights with Daenerys against the Sons of the Harpy during their surprise ambush at Daznak's Pit. After Daenerys flies away on the back of her dragon Drogon, Aegon elects to remain in Meereen with Tyrion, Jon Connington (who arrived in Meereen alongside Varys), Missandei, and Grey Worm.
Following Daenerys's disappearance, Aegon stays behind in Meereen and serves as Tyrion's apprentice, to learn about politics and on how to rule, if Daenerys never returns. Therefore, he becomes acting Prince of Meereen in her absence.
Aegon is well educated and intelligent, speaking several languages, and is well versed in history. He speaks the Common Tongue as a native speaker. He is fluent in High Valyrian, in the Bastard Valyrian dialects of Pentos, Tyrosh, Myr, and Lys, and in Trade Talk. He is a novice at speaking the dialect of Volantis, only familiar with a few of its words. The dialect of Meereen, whose terms derive from both Valyrian and Ghiscari, gives him trouble. He has some training in mathematics, with a decent knowledge of sums and a limited understanding of geometry. He also has been trained in songs. Tyrion notes that Aegon is more learned than "half the lords in Westeros".