|Although this article is based on canonical information, the actual name of this subject is pure conjecture.
- "Rook's Rest had left Aegon bent and twisted, his once handsome face puffy from milk of the poppy, with burn scars covering half his body. Rhaenyra, ever defiant, told her dear brother that she'd hoped he was dead. "After you!", Aegon answered."
- ―Joffrey Baratheon
When Rhaenyra and her husband Daemon conquered King's Landing, they found and imprisoned the whole family and counselors of Aegon II. But Aegon himself, convalescing from his wounds he sustained in battle of Rook's Rest, had disappeared from the city with his Kingsguard and his badly wounded dragon Sunfyre.A few months after taking the Iron Throne, Rhaenyra received the news of the death of her husband while commoners in the capital rose in a rebellion to kill the dragons who they believed to be root cause of the troubles in the Seven Kingdoms.Prince Joffrey, Rhaenyra's eldest surviving son, tried to rescue the dragons in the Dragonpit, including his personal dragon Tyraxes, by mounting Rhaenyra's own personal dragon Syrax. Syrax, who would only take Rhaenyra as a mount, threw off Joffrey, who fell to his death, but Syrax continued on to the Dragonpit attracted by the bloodshed. The rioters killed all the dragons including Syrax and plunged the city into chaos. Rhaenyra, fearing for her own life and that of her surviving son Aegon, escaped to Dragonstone by selling her crown for a passage by boat with her remaining supporters.
The AmbushJust as Rhaenyra set foot on Dragonstone, she was seized along with her son and her remaining guards were killed by Dragonstone's guards who had secretly taken Dragonstone for Aegon. Rhaenyra was then led into Dragonstone's throne room to find King Aegon seated on the throne flanked by his dying dragon Sunfyre. The rival siblings exchanged brief words with Rhaenyra proving she still did not fear Aegon. He then ordered Sunfyre to devour his sister alive in front of her horrified son. The dragon first incinerated Rhaenyra, then ate the body leaving behind only her legs on the throne room's floor.
AftermathAegon took the surviving son of Rhaenyra, Aegon the Younger, hostage and returned with him to King's Landing to sit on the Iron Throne as the only king of the Seven Kingdoms. But Rhaenyra's faction did not surrender after her death and continued the fight until approaching the doors of the capital a half-year later. The refusal of the king to surrender led to his own servants to poison him and to appoint his nephew (and Rhaenyra's son) king, putting an end to the war.
Witnessing a dragon kill his mother traumatized Aegon the Younger so much that he developed an incurable fear of the dragons. He never again rode a dragon and during his reign the few dragons that survived the war were dying younger every time. Many suspected that Aegon himself was responsible for poisoning them so that history would remember him as Aegon Dragonsbane. Beyond his fear of the beasts of his own sigil, Aegon III was remembered as a king who avoided human contact and a victim of his incurable melancholy.
In the books
Prelude: Fall of Dragonstone
Around the time of First Battle of Tumbleton, the merchant cog Nessaria made a stop at Dragonstone for repairs and provisions, having been driven off course by a storm. They spotted two fighting dragons while passing the Dragonmont. Inspired by the story from those of Volantis, local fishermen took their boats for a look the next morning, and they reported the burned and broken remains of the Grey Ghost. Ser Robert Quince, Dragonstone's castellan, named the Cannibal as the killer.
Lord Larys Strong had disguised King Aegon II during the fall of King's Landing and smuggled him to Dragonstone, where Aegon was later found by Sunfyre. It had been Aegon's dragon who had actually killed the Grey Ghost, not the Cannibal. Rider and dragon went out flying again, regaining strength, while Aegon's supporters found locals willing to betray Rhaenyra, due to dislike for her.
Poorly-defended Dragonstone fell easily, with Robert being slain by Ser Alfred Broome, who was angered at not being named castellan by Rhaenyra. Lady Baela, Prince Daemon's daughter, tried to escape her attackers on her dragon, Moondancer. But Sunfyre blinded Moondancer with fire and eventually killed the younger dragon after she crashed to the ground. The burned and battered Baela was taken captive and King Aegon the Elder now held Dragonstone, although he broke his legs in the fighting. 
Not long after taking Dragonstone, Raven reached Aegon II regarding Rhaenyra's return to Dragonstone. This gave Aegon the opportunity to prepare for her arrival.
Flight and ambush of Rhaenyra
After the Storming of the Dragonpit, Rhaenyra's councilors agreed that the city was lost. She was persuaded to leave the next day, slipping through the Dragon Gate for Duskendale. Rhaenyra Targaryen was refused entry at Rosby and was allowed to stay only one night at Stokeworth, half her gold cloaks deserted on the road, and attackers killed several of her knights. At Duskendale they were admitted, but not allowed to stay long. Refusing to part from her son, Aegon the Younger, and without ships, Rhaenyra sold her crown to buy passage on a Braavosi ship. She returned to Dragonstone, hoping to hatch a new dragon from the island's dragon eggs .
Ser Alfred Broome and his garrison killed Rhaenyra's remaining men and captured the queen, her ladies, and Aegon the Younger. Once inside the gates, Rhaenyra faced Aegon II Targaryen and the wounded Sunfyre. Aegon the Elder fed Rhaenyra to his dragon while Aegon the Younger looked on. With the chance that Rhaenyra's loyalists would continue the fight in her son's name, Aegon the Younger became a hostage. It was the twenty-second day of the tenth month of 130 AC.
On the ninth day of the twelfth month, Sunfyre the Golden died on Dragonstone. After this, Aegon started planning his return to King's Landing. Though Rhaenyra had died, her cause lived on. Aegon II would sit the throne again, but it would only last another half of a year.