Brynn Myers said this quote

The prophecy stated that Hades' most beloved oracle, Sybil, was to bed two males of significance on the same night. Each male had been chosen from the finest of all Hades' demons to consecrate this union. They were to fill her not only their seed but with their blood, giving the boys their life and their abilities. On the day of their birth, Sybil announced that her boys were to rule the five rivers and would do so in peace for many years, but that eventually, one of her sons would become the underworld's demise, while the other would become its destiny.