No, they are not related in any way. Risher is a person who was taken in by the king because his omega father was the king's first love. The prince was born from the king and the queen. He called the prince brother BC they knew eachother since young and the prince was a bit older than him.
However, don't read it yet. It is still in the peak or just the start of conflict between the prince and his "mother". Let it marinade for a while.
It was supposes to be hyung or smth but they translated it, from what i know hyung is a term to someone older than you that is very close to you or smth
Before I get further into this is this incest? Rishar calls him brother and although I know their not directly related are they blood related?