Consort is also a legal wife but he's powerless against Nathaniel in terms of power and position. Nathaniel's only threatened by his presence because he may have the potential to have an heir (repeatedly called heir because Nathaniel sees children bore by him and the king as a tool and security to his position as Queen) It will only be called "Child" if the Nathaniel actually loves the King but reading from the novel (Novel is actually more accurate to say what Nathaniel feels to the king and in the novel, it is obvious that he never had any feelings for him and just wanted to get it done and be over it)
Also dw, he found his match later on

Agshdjskl.. I don't know what to say, I feel so conflicted since mc is the consort
I'm waiting for the baby