I forgot the title but I remember the hero already killed the demon queen who's a fujoshi (lol) who kidnapped the prince and even made him dress up as a bride to marry an orc (ewww). The story start with the (idiot) king and his subjects wanting to believe the hero's loyality but can't. So they want him to marry him to a princess. The problem that their country havve nothing but princes. Making him into the son in-law of another powerful family will be a threat to the throne, marrying him into a lower-ranked family would anger the citiziens who love him too much. The stupid result of reaching out to the prince's crazy fangirl (who's the mage who have gone with the hero on his journey) is that they decided to make the prince a girl with a potion. The king is an idiot, the mage is a creepy stalker, the queen is too devoted to her husband that she's okay with making her son a daughter, the citiziens idolize the prince like workshippers, the female knight is a pervert, the saint is a slut, the hero and prince(ss) are the only decent ones it seems.
I Became the Hero’s Bride! Idk i don't read the novel, but your description seems fit in the spoiler i found.