Following the death of King Viserys I Targaryen, a war for succession begins.

Prince Aegon II eventually takes the throne, meaning Princes Helaena becomes the queen. Princess Rhaenyra rejects this outcome and crowns herself as Queen of the Seven Kingdoms on Dragonstone. Helaena refuses to swear her allegiance to Rhaenyra, and as a result, Prince Daemon Targaryen hires two assassins, Blood and Cheese, to murder one of her sons.

Source: https://www.distractify.com/p/aegon-targaryen-wife