Killermare was 14 or 15 yrs old, the child of Nightmare

Killermare walks inside the castle's corridors to the throne room. As they enter the room Nightmare was sitting on his throne chair with his elbow on the armchair while his head resting on his fist, Dust, Killer and Horror were leaning behind the wall and Cross was sitting on the floor beside Nightmare and Error is sitting on his hammock swing that is made of his blue strings on the ceiling

Nightmare: "what is it, child?"