Merlin never returned to Camelot.
As much as he loved his home and his friends—Gaius, Gwen, the knights—his first and final duty would always be with his King. The Once and Future King.
So, he waited.
He saw the world pass him by, watched as magic sunk deep into the earth and the secret places of the Old Religion faded into the darkness of aging forests. The Camelot of his youth passed into history, then into legend. With each age, Merlin was there to make sure that the stories were heard and loved, and that King Arthur was never forgotten.
He watched the rulers of Albion rise and fall. He saw countless days of war and grief and strife. Every battle seemed worse than the last, and with each new atrocity he thought that now must be the time for the King's return.
But through a thousand years and more, nothing happened.
Until one day, it did.
In a time of hatred, darkness, and despair beyond grief, a time when all the goodness and light and magic seemed lost from the world, he came back.
He came like the golden light of dawn after the longest night of winter, like the first birdsong of spring, like a spark that ignites an unstoppable blaze.
Like the sight of a treasured, much-missed friend.
And Merlin was there, waiting.
The gnarled old man watched as the golden haired king walked out of the mists of legend and into a world in need of help.
The two regarded each other for a long moment without speaking.
"Merlin," said Arthur, smiling. "Well done."
The old wizard rushed forward and embraced his friend, sobbing unrestrainedly. After a moment, they broke apart, and Arthur examined the sorcerer at arm's length.
"The others send their love," the King said. "And Gwaine wanted me to say that the beard is not a good look for you."
Merlin laughed through his tears, and as he laughed, his age melted away until he was once more the dark-haired boy of so many years ago.
"I'm sorry," the warlock said, wiping his eyes. "I've just been waiting for a long time."
"We've all missed you too," Arthur said, gripping Merlin's shoulder. "Gwen, Gaius, they all can't wait to see you again."
"Will they?" Merlin asked, eyes wide and vulnerable. "Can I go were they are?"
"Of course," said Arthur bracingly. "Once our task is complete, we'll both go. Do you honestly think a faithful servant like you would be turned away? I did promise you a day off, after all."
"As I remember," said Merlin, eyes narrowing, "It was two days off."
"Two days off?" Arthur scoffed "Really, Merlin, I think you've gone a bit senile."
"Then I don't suppose you'll want my help to save the kingdom, will you, sire?"
"Well, I'm sure I don't need your help, but since you've been here lazing about for centuries…"
"You know, I should have told that White fellow to title his book 'The Once and Future Prat.' It would've been more fitting."
Arthur laughed, then turned to face the strange new world before him. Merlin stood at his side, finally back where he belonged.
"Come on, Merlin. Let's make some more legends."