This is quite common for nobles to marry and spend intimacy with their cousins. So to them, it is not incest. Helps keep the bloodline strong and not mix blood with someone unrelated.
Of course in this story, I diubt it was supposed to go that way but now with those two spending the night together, they have no choice but to get them engaged.
It’s supposed to be second cousins they are first cousins. So your mom‘s sister son is off-limits but your grandmother‘s sisters son is fair game.
Inbreeding is very common on nobility, to protect the "pureness" Of their blood, disgusting really..
The House of Habsburg (specifically the Spanish branch) is the most famous royal family that declined and eventually died out due to centuries of intensive inbreeding and accumulated genetic disorders. It’s actually a very long and deep 200 years of first cousins and uncle nieces marriages.
One of the reasons why I started reading HisRom stories was because I was expecting some realistic genetic disorders in it. They can't even step on that hill when they wanted to include incest in it like bro...
Wait isn't this incest? Like isn't she their cousin? Please tell me if I'm wrong and I'm really hoping I'm wrong