Read manga: The Hero Became The Duke's Eldest Son

manga
Summary:

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?