- "Rhaenyra was dead and King Aegon sat the Iron Throne again. But only for half a year. He was poisoned by his own men and replaced with the very boy who had watched his mother devoured."
- ―Viserys Targaryen
The Assassination of Aegon II was the conclusion of the civil war in the Seven Kingdoms known as the Dance of Dragons. The death of King Aegon II took place in the hall of the Iron Throne and subsequent coronation of his hostage nephew Aegon III facilitated the end of hostilities between the Blacks and the Greens.
Following the Ambush at Dragonstone, Rhaenyra Targaryen had been killed and her son, Aegon Targaryen, had been named heir to Aegon II Targaryen. However, the remainder of Aegon II's reign was not pleasant, as he had a mental infliction due to regular consumption of Milk of the poppy from his injuries at the Siege of Rook's Rest.
This led to the ascension of Aegon III Targaryen, who would effectively end the initial fear possessed by the Targaryens created through their dragons, as the last dragon died under his reign, becoming known as "The Dragonbane".
In the books
In the A Song of Ice and Fire novles, once King's Landing was secured for King Aegon II Targaryen, Lord Borros Baratheon led his armies against the Rivermen who were approaching the city on the Kingsroad. These Lads were led by Lord Kermit Tully, Lord Benjicot Blackwood, and Ben's aunt Alysanne Blackwood. Bloody Ben Blackwood broke the flank of the confident Borros, and "Black Aly" led the archers that brought down Borros's knights. Lord Baratheon killed Lords Darry and Mallister, before he himself was killed by Lord Tully.
This left King's Landing with only meager defenses, with the Lads only a short distance away. Lord Cregan Stark and his forces marched south to reinforce them.
When the Black army of the Lads was a day's march outside of King's Landing, there were no significant green forces to stop them. Lord Cregan Stark was coming south, and other armies were coming from The Vale of Arryn as well. King Aegon II Targaryen refused to surrender, even when Lord Corlys Velaryon, now Master of Ships on Aegon's Small Council, advised him that the only remaining option was to surrender and join the Night's Watch. Instead, Aegon gave orders to have cut off the ear of his nephew, Aegon the Younger, and have it sent to the Lads as a warning—if his bloodline died, so would Rhaenyra's. Aegon II was shortly found dead shortly after, with blood on his lips from poisoned wine. Who poisoned the king remains unknown, though twenty-two men would be arrested.
With King Aegon II Targaryen dead, Aegon the Younger was crowned as King Aegon III Targaryen. Although Aegon II's host had been defeated and the Velaryon fleet once more served the Iron Throne, the period that followed was named the False Dawn.
The realm faced numerous problems. The cruel winter that had begun the year before on Maiden's Day of 130 AC would last until 135 AC. Much of the realm had been burned out by dragonfire - in particular, Aemond Targaryen's one-man war riding Vhagar, which had burned out most of the Riverlands. Broken men and outlaws roamed the countryside in the hundreds and thousands, and public order had collapsed in many places. The ironborn, under the command of Dalton Greyjoy — who had only nominally sided with the Blacks as a pretext to attack wealthy Green kingdoms — now refused to acknowledge the boy-king Aegon III's commands to stop raiding.
Lord Cregan Stark and his northern army of childless, homeless, and younger men had marched to King's Landing with hopes of adventure. The sudden death of King Aegon II had robbed them of that chance, leaving Cregan furious. He had wanted to punish Storm's End, Casterly Rock and Oldtown for having supported Aegon II over Rhaenyra, but upon his arrival, Lord Corlys Velaryon had already sent out ravens, suing for peace.
Lord Cregan Stark could not be dissuaded in punishing the betrayers and poisoners of King Aegon II Targaryen. He found the poisoning foul murder, and had twenty-two men arrested in the name of young Aegon III Targaryen, including Lords Larys Strong and Corlys Velaryon. He then made Aegon name him Hand of the King.
Cregan reigned as Hand during a day filled with trials and executions. Most of those accused chose to take the Black—chief among them, Ser Perkin the Flea — but Ser Gyles Belgrave of the Kingsguard and Larys chose death. Corlys was spared a trial thanks to the intervention of Baela and Rhaena Targaryen. The day after the executions, Cregan resigned as Hand and returned to the north, leaving many of his northmen behind in the south.