The Hero Became the Duke's Eldest Son

Aden Albireo, the "Dragon Slayer King", was a hero who saved the world by eliminating the Berserker and the Underlord. However, he was betrayed by those who whispered friendship to him, and met his death... "I didn't know I would be resurrected like this?!" 15 years before the Underlord's resurrection, 'Aden Albireo' reincarnated into the body of the eldest son of a unheard-of duke's family, 'Aden Remes'! And... "It's been a while, Dragon Slayer King!" "The Underlord I thought I had defeated is inside my soul?!" Will Aden be able to end his uncomfortable cohabitation(?) with the Underlord and prevent his resurrection?