I believe the child Rasta had was not his because they did a blood test to check paternity. But after Rasta had her trial and the baby was taken away the Duke try to create doubt in the King by saying the results were fake in order to undermine him. I'm pretty sure the king may be sterile.
Well there is the fact that Rashta just wanted security for herself and children but... she got ambitious and when she started to send assasins to kill the Empress, she went too far. She went mad with power but... that is because she didn't know what to do with it. The Emepror put too much on her without any real support and taking for the fact she was not qualified. She also tried to cut off the innocent maids tongue out for discovering blue feathers under pillow... you can sense the decent into madness with her.
SPOILER KINDA
Other people are saying it’s some other guys but then I asked my friend and they said it was actually his and that the person who said it wasnt was lying? IM CONFUSED BUT EITHER WAY I FEEL ANGER AT THE KING HES SO FUCKING ANNOYING. I do feel somewhat bad for ratasha, but I can’t see myself ever supporting her relationship with the king. Sorry ratasha stans I hope I didn’t offend ya’ll