What society?
As long as the reigning ruler gives them the blessing and approve their relationship, then no one can stop Eugene from marrying Hari. Besides, he's a duke, and a duke with special ties with the royal family no less.
but ppl still considered them as SIBLINGS even the royal fam eventho they r close
I read the novel. The backlash isn't as severe from the high society, because Eugene is a powerful duke, and Hari has a powerful influence and still a well respected noble lady, especially since these two are supported by the crown prince.
Besides it's not unheard of that past monarchs in our world haven't indulge in incest anyways, just to keep the bloodline pure. High aristocrats(like marquis and above) probably indulge in incest as well, like marrying their first cousins or something to either maintain their power, if their family can't advance further by marrying other families of higher status.
Considering the webtoon setting have royals and aristocracy then the society back then pretty much dated in the medieval period. A different society than our modern ones.
honestly.. you know how society works right ? im pretty sure even if hari and eugene love each other they cant marry yk.. bc the society and also their fam saw them as big brother and little sister.. also ive this feeling that the crown prince is going to marry hari ??