
Hear me out....what if...she is related to the crown prince?? Like, maybe she is like a bastard child of the king and that is the "secret of her birth" yes?
And that is why the prince's mother hates the MC and the prince wants to give her status his mother cannot touch, yes?
Maybe I'm tripping, but I don't know why the prince's obsession gives me "incest"

*spoiler*
Ding ding ding!’ You’re correct but they’re actually cousins. The Queen’s younger sister got seduced and discarded by the duke who was instructed by the queen. The prince knows this and is trying to take out anyone who knows the history…
He’s down bad for his cousin I guess!! First cousin too eww

I'm not enabling it by no means, but isn't this era known for "keeping it in the family"? Lmfaooo! I know it's rofan, but y'know what I mean? It's not mainstream, but at the very least they kind of brush it off?? Or idk, maybe this particular manhwa doesn't have that concept, it honestly depends. But irl, yes it does

Although incest is something that is common throughout history, it was generally seen as odd even then. It was mainly something that happened in royal family's/marriages but it wouldn't be as direct as a first cousin, they mainly went third and above so as to not cause any development issues for the offspring. It was also common in royal families because almost all Royals were related to each somehow, there were only so many European royal familes that could be married into, before they knew it they were all related. (Sorry for the rant )
"I'll even marry you for real" every bottom's famous last words