Great Council of 101
From A Wiki of Ice and Fire
The Great Council of 101 took place in 101AL at Harrenhal. After the death of King Jaehaerys I's heir, Baelon Targaryen, a Great Council was held to answer the question of who should succeed the Old King.
Candidates for the crown included Princess Rhaenys Targaryen, Prince Viserys Targaryen, Ser Laenor Velaryon, and Lady Laena Velaryon. The lords assembled favored the male claimant over the female by twenty to one, although supporters of Rhaenys included Houses Baratheon, Stark, Dustin, and Manderly. Viserys Targaryen was ultimately chosen by the assembled nobility.
Following the death of King Viserys I, his small council examined the annals of the Great Council. They determined that the houses which had dissented during the Great Council were likely to support the claim of Rhaenyra Targaryen instead of Aegon II Targaryen.