Kaldrek Stormwarden as the somewhat inhuman Court Sorcerer served the King as one of his most trusted advisors. He had also been the king's best friend since they were children.
Perhaps that is why the king couldn't leave him alone and actually forced him to get married.
Zylvia was an orphan of indeterminate origin who had been found and raised by a couple who were incapable of having children. Her unnatural looks had often ostracized her from other people and she didn't have that many friends. She did however have a best friend who she did everything with. This friend ended up marrying the king and becoming queen.
Her friendship with the queen is probably the reason why their meddling king chose her to marry his best friend. After all it would please his lovely queen if she could see her best friend every day.