Hero's Marriage

in a fantasy kingdom, "platinum" defeated the demon king and was crowned the hero, without knowing that the kingdom's princess is the reward for defeating the demon king... tl note: i don't know if this already exists here, nor do i know the author of this. i found this through chinese translations, where they listed the author as sherlyn. i'm not sure if that's accurate though. don't change this to chinese. the source is japanese goddammit, look at his/her twitter author twitter: https://twitter.com/HakkouAin