He awoke with a start. The magic within the Earth was humming in distress. It was a sensation he hadn't experienced in hundreds of years especially since the Old Religion had gone into decline and the weaker use of wand magic had become prevalent. He groaned in despair; all he wanted was to be left alone to sleep in peace as the decades moved on around him.
Nearly every one of his friends and loved ones had either died or moved away after the death of King Arthur and the fall of the city soon followed. Not being able to witness the destruction of his home he went into hiding and stayed in a state of depression for many years. His mental state was worsened by the realisation of his immortality. His physical appearance didn't age above 30 while he just wanted to wither and die in his secluded cave.
Eventually, he overcame the feeling of hopelessness and slowly began to make appearances in settlements around the country, making sure to never stay in one place for too long or to become too attached to anyone as this would make leaving much harder. He experienced many occupations over the years and saw the development of different lifestyles, fashions and technologies.
Over the centuries the Triple Goddess would send him signals if a major magical event was about to take place. The most significant was the construction of a school for magical children called Hogwarts. The four founders of the school were extremely talented in the magic that had become commonplace. Even though their magic was a much weakened version of the kind he used, they were as powerful as some of the sorcerers he had come into contact with back in Camelot. Their unusual amount of power and their goal to build a school of magic was what persuaded him to keep an eye on their development from the shadows. He watched and gave a small amount of aid as their dream became reality and Hogwarts School of Witchcraft and Wizardry was opened.
After this major magical feat, he once again reclined to the familiar comfort of his cave, where he put a spell on himself to only be woken up by important signals sent to him by the Triple Goddess, and fell into a deep slumber lasting for hundreds of years.
Unenthusiastically, he trudged over to his crystal ball, gifted to him by a messenger of the Triple Goddess. It displayed images from what he assumed was events from recent years. A war between people of magic on a massive scale; death and destruction; an evil archetypal super-villain who going by the name 'Lord Voldemort'. Finally, the images showed the life of a young boy whose parents had been murdered when he was just a small child. They showed his dreadful upbringing until he received his letter from Hogwarts at the age of 11 and his whole world changed. The crystal ball continued to display his journey though Hogwarts until it reached his fourth year and the Triwizard Tournament.
He immediately knew why these images were important when the incident in the graveyard took place. Lord Voldemort had fully risen once again and he needed to intervene. Merlin was going to Hogwarts.