While touring the Great Sept of Baelor in King's Landing, King Joffrey Baratheon explains to Margaery Tyrell that Rhaenyra Targaryen was eaten by her brother's dragon while her son - Aegon III, whom he doesn't mention by name - was forced to watch.
In the books
In the A Song of Ice and Fire novels, Aegon III watched as his mother was devoured by the dragon of Aegon II, his uncle, during the civil war known as the Dance of Dragons. Due to the trauma of witnessing his mother's death, Aegon III developed a fierce hatred and terror of the creatures.
Aegon III ascended to the Iron Throne after Aegon II died without any males heirs. He married Aegon II's surviving daughter to seal the peace between the two rival branches of House Targaryen. He ruled the Seven Kingdoms long and well, though he is often blamed for the death of the last dragon, for which he became known as "Aegon the Dragonbane" despite his later efforts to obtain Dragon eggs. At some point he had nine mages cross the sea to attempt to hatch his remaining cache of eggs.
Aegon had two sons: Daeron, called the Young Dragon, and Baelor, called Baelor the Blessed, and among his daughters were the three "Maidens in the Tower," Daena the Defiant, Rhaena and Elaena. Upon his death in 157AL, Aegon III was succeeded by his young son Daeron. Aegon was said to have always walked with a great grief, and the folly of his sons nearly tore the realm apart.
- Aegon III Targaryen at A Wiki of Ice and Fire (MAJOR spoilers from the books)
|Lord:||Queen Daenerys Targaryen||Heir:||None|
|Title(s):||King of the Andals and the First Men|
|Ancestors:||Aegon the Conqueror · Visenya · Rhaenys · Maegor the Cruel · Jaehaerys I · Rhaenyra · Aegon II · Aegon III · Daeron the Young Dragon · Baelor the Blessed · Viserys II · Aegon the Unworthy · Naerys · Daena the Defiant · Rhaena · Elaena · Daeron the Good · Daenerys Martell · Myriah Martell · Baelor Breakspear · Aerys I · Aelinor · Rhaegel · Maekar I · Aerion the Monstrous · Aegon the Unlikely · Duncan the Small|
|Current members:||Aemon Targaryen|
|Deceased members:||Aerys II Targaryen · Rhaella Targaryen · Rhaegar Targaryen · Elia Martell · Rhaenys Targaryen · Aegon Targaryen · Viserys Targaryen · Drogo · Rhaego|
|Household:||Ser Jorah Mormont · Ser Barristan Selmy · Rakharo · Kovarro · Aggo · Irri · Doreah · Jhiqui · Malakho · Missandei · Grey Worm · Daario Naharis|
Kings of Westeros
Aegon I, the Conqueror · Maegor I, the Cruel · Jaehaerys I, the Conciliator · Aegon II · Aegon III, the Dragonbane · Daeron I, the Young Dragon · Baelor I, the Blessed · Viserys II · Aegon IV, the Unworthy · Daeron II, the Good · Aerys I · Maekar I · Aegon V, the Unlikely · Aerys II, the Mad