Ernest Macmillan was the Lieutenant of Hufflepuff for the DA. He married Susan Bones over the Christmas Holidays. She later became pregnant with his daughter, but Ernie would never live to see Cecily Harriet Macmillan born. During the Battle of Hogwarts Sue was dying but Ernie used old Celtic magic to give his life to Sue, so that Sue would live (and could have their child) and he would die. But Ernie would become a ghost tethered to Cecily, so he went with Cecily everywhere, and Cecily could see him but others couldn't (though when Cecily grew older she couldn't see him either).