A scene from “Unfinished Business”

Rhaenyra: As the first century of the Targaryen dynasty came to a close, the health of the Old King, Jaehaerys, was failing. In those days, House Targaryen stood at the height of its strength, with ten adult dragons under its yoke. No power in the world could stand against it. King Jaehaerys reigned over nearly sixty years of peace and prosperity, but tragedy had claimed both his sons, leaving his succession in doubt. So, in the year 101, the Old King called a Great Council to choose an heir. Over a thousand lords made the journey to Harrenhal. Fourteen succession claims were heard, but only two were truly considered. Rhaenys, the King's eldest descendant, and her younger cousin, Prince Viserys Targaryen, the King's eldest male descendant.

King Jaehaerys I Targaryen: [flashback, the day of the Great Council] It is declared by all lords paramount and lords vassal of the Seven Kingdoms that Prince Viserys Targaryen be made Prince of Dragonstone.

Rhaenyra: Rhaenys, a woman, would not inherit the Iron Throne. The lords instead chose Viserys, my father. Jaehaerys called the Great Council to prevent a war being fought over his succession. For he knew the cold truth. The only thing that could tear down the House of the Dragon was itself.