I'm not sure... I remember the previous King loves and is so obsess with the previous Duke Cadiff's wife to the point that he used his authority as King to force the wife to give birth to the Current King, the previous duke agreed.. The current king actually didn't bear any resemblance from the previous king, but did get his mother's red hair.. There were rumors that the current King isn't actually the previous king's son..
As for the Current Duke of the Cadiff Household, Arthur, was born after the previous King's order for her to give birth of his child was fulfilled.. The Cadiff House has two kids btw.. One is Arthur and the other one was their youngest sister..
All in all, The Current King is the Half-brother of the Current Duke Cadiff, Arthur..
I know the current King is also a victim of their parents' choices.. But Idk, I still don't quite like him.. Probably cuz he being a creep rn.. But I read a lil spoiler somewhere in Novel Updates a few months ago that he will change for the betterrrr~
Wait shit, forget every thing that I typed above.. I reread some spoilers in Novel Updates...
•
•
•
•
Arthur was the only son of the former Duke Cardiff, who died when he was eleven. The Duke was loyal and brave, while the Duchess most beautiful woman in the kingdom. They were loved by all the residents. The former king kidnaped the duke and said to the duchess that if she wants her husband she had to marry him. She entered the palace to save her husband. The former emperor used to be calm and rational but after falling in love with the duchess he lost all rationality. The former duke escaped and got the duchess who already gave birth to the current king (Red hair, yellow eyes). Arthur was born after the whole fiasco. They grew up together but they have a complicated relationship.

So we know that Arthur is the son of the previous king, but is king the son of duke? But there's no alike of all. Did the duchess cheated or got raped? Hmm, mystery