If a king decrees it inside an absolute monarchy, it's not a crime. That's literally how absolute monarchies work--the monarch has absolute and unaccountable power.

Edit: if you disagree, please tell me why.

I disagree because positivism is not the smartest legal theory in my view. We all know Godwin's law, but nazi crimes is probably the best example of how something done by people with absolute power was considered and persecuted as a crime.