"Which brings us neatly to him," said Harry. "History became legend over the centuries, Hermione. Different writers embellished the story and the truth got buried somewhere. The reality is that Merlin was part of a triad relationship with Uther Pendragon and his wife, Igraine. Uther saw the advantage of having an offspring with powerful magical skill, so Merlin sired Arthur with Igraine. He's his true father. When Merlin was betrayed and murdered by one of his apprentices, Uther adopted Arthur as his own and the legend was born.