Minerva McGonnagall was made headmistress of Hogwarts after the final battle. When the castle reopens in September she is visited by the head elf, Boris. Boris has a very familiar look to him that she cannot place at first. Boris tells her of the traditions surrounding the head elf and how they are not decided upon but born and that she will be the one to give birth to the next head elf and that he will sire it. This is tradition that has been taking place since the beginning of Hogwarts, and it is then she realises that Boris looks familiar as he is Albus child.