The overall goal of the campaign and the party is to bring down the current Invincible Overlord of the Citystate. Hygelak the XI, was the 16th son of the previous Overlord, and had no chance of inheriting the title. Not only did he kill several of his older half-brothers in duels, he also went into self-exile. He returned to the Citystate when his father was in the middle of the battle and helped turn the tide. Bypassing several siblings older than him, the Overlord declared him his new heir.
He is your uncle, and he took your chance of ruling.