To be honest, Doro's excuse is really bad.
It's so bad that even in such a serious situation, Adeline feels like laughing.
Honestly speaking, even if he said he had fallen for the Demon King and married her, it would be more believable than this "being the Apostle of the Demon King." After all, having met in person, Adeline genuinely felt the demonic charm of the current Demon King; the Demon King's demonic aura could indeed be captivating.
But being the Apostle of the Demon King...?
If you grabbed someone randomly on the street and asked them if it's possible for the Hero to become the Apostle of the Demon King, they'd just spit at you.
Anyone who's heard of the Hero's adventure stories, even the simplest farmers, could throw a few reasons at you why the Hero couldn't possibly become the Apostle of the Demon King—after all, A·Gedora is stronger.
Because A·Gedora killed the Demon King.
