Sorry but I don't think that's what happened his wife was killed together with her family after a undisclosed scandal/crime occurred
He them seduced the princess to marry her and kill the late emperor and the princess and place his son as a heir to the empire
Apparently she was genuinely in love with him and treated his son as her own
I don't believe the royal family was innocent, they hold so much power over people it's laughable. Just seeing how the emperor referred to the son says a lot about their relationship.
It doesn't matter how much the princess loved the guy, her family killed his lover. Do you think the royal family trusted an outsider so much that they let him marry into them after getting his SO killed? Maybe she didn't know why she died and truly wanted to help him but her father did know and let him in. Why would he put her daughter in danger by allowing her to marry a dude that'll probably try to murder her in her sleep.
Again, the only that's truly innocent is the FL, fuck the rest of them.
The royal family killing his lover/wife so the princess could play house? shit, imagine your SO getting killed, just as you started a family with them, because a royal dipshit wants you all to themselves. Then having them take on the role of your child's parent. Cynical bitch holy shit. I mean, the FL dad's abusing an innocent child that didn't ask to be born is horrible and fuck him...but I can understand why he wants to get rid of the bloodline all together.