Body swap with cinderella beats, a king that only thinks with his dick and is obviously retarded, a too good for school redheaded dude, a meek princess, two asshole daughters that think they are more royal than royal honey but are as common as used toilet paper and the oh so trusty marriagable candidate excuse to send you away because I obviously don't want you and your solid right of succession near me and my used toilet paper of daughters that are obviously from different fathers each.
Princess then turns into savage princess (because of being a dude on the inside) and gets to trouble the killer queen time and time again until she bites the dust along with her daughters, then of course the prince (pirncess) also passes through some trials and becomes more calm but actually able to stand up for himself and be mindful/empathetic which makes him even more likely to be king due to the effect that attitude has on the people (oh he is nice I want him as king even more yay!).
The swap is reversed retarded king has the only good idea he had in his entire life and uses his actual head to abdicate after looking at the mess he caused and leaves everything to the new powercouple.
Expect some tanned prince from a faraway land falling in love with the princess(dude) because of her personality (a dude) at the middle and some war with the EMPIRE because there is ALWAYS an EMPIRE and the daughter of the emperor falls in love (or wants as a pet because empire=evil) with the prince(girl) because of his charm (a girl). Then both secondary drama inducers discover that they have been in the closet all along and create a world where everyone can love everyone and kings who think with their gonads are castrated and then forced to live as the people they ruined their lives.
The end.
Prove me wrong manhwa!!! Because I'll read you til the end!!!