When news of the disaster at the Trident reached King's Landing, Lord Tywin Lannister of Casterly Rock, who had kept the west out of the war and waited upon its outcome, at last marched his host of some twelve thousand men to the gates of the capital and professed his loyalty to King Aerys. The Mad King, mistrustful yet desperate, took the counsel of Grand Maester Pycelle and opened his gates to the lions. It was a fatal error. Once inside the walls, Tywin's men threw off the pretense and sacked the city in Robert Baratheon's name, putting the smallfolk to the sword and the torch and storming the Red Keep itself.
The horror of that day would stain the honor of House Lannister for a generation. Ser Gregor Clegane, called the Mountain That Rides, and Ser Amory Lorch broke into the royal apartments: Lorch cut down the little princess Rhaenys where she hid beneath her father's bed, and Clegane dashed out the brains of the infant prince Aegon and then raped and murdered his mother, the Dornish princess Elia Martell, upon the bodies of her children. King Aerys II himself was slain in the throne room by Ser Jaime Lannister of his own Kingsguard, who opened the king's throat rather than obey the command to burn the city with the wildfire caches hidden beneath it; for that deed Jaime would be called Kingslayer ever after, and was found seated upon the Iron Throne when the rebels arrived.
When Lord Eddard Stark reached the capital he found Tywin Lannister's banners already flying and the murdered children wrapped in crimson cloaks laid before Robert as a gift of loyalty. Robert would not condemn the killings, judging them the necessary end of dragonspawn, and the bitter quarrel that followed drove Ned from the city in anger and cast a long shadow over the reign that the sack had won. The Targaryen dynasty, near three hundred years upon the Iron Throne, ended in the blood of that day.