I own neither the BBC series nor the ancient legend that has lived for centuries and will live for centuries more.
Consider yourself warned; this contains serious mentions of character death. If it helps, the story spans years and years in true fairy-tale fashion.
The King never married.
The general gossip was that his foster-sister's defection to Black Sorcery had completely destroyed his ability to trust women with his heart. The gossip said that he had loved her—even though the documents were never drawn up, it had been clear from the moment the former king's foster-daughter set foot in Camelot that the two royals were intended for each other.
The former servant of the King, the one and only legal Warlock in the entirety of Camelot, married the former servant of the King's foster-sister.
The gossips approved of this match. While the warlock in question was one of the most powerful men in Albion in both influence and sheer magical power, he was low-born, and like should wed like, even in such a progressive city as Camelot. The wedding was relatively quiet—just public enough to show that the wedding was not to cover up a scandal, and just private enough out of respect to the groom's unwed best friend and sovereign. The couple settled down marvelously quickly as well—never arguing, never upset with each other. They were good friends in addition to being spouses, and everyone admired this show of domestic bliss.
What the gossips didn't know was that the house in the better-off outskirts of the city—a gift from said best friend and sovereign—had two bedrooms. No one saw that two sets of linens were washed on laundry day; the warlock took full advantage of his ability to magically clean things to the point where they appeared and felt new, and the two former servants felt no need to hire ones themselves. The gossips didn't question the fact that the King was often seen going to visit late at night. It was his friend's and advisor's house, and the gossips said that it showed how good a king he was, going to visit his friends instead of ordering them to come to him.
They also didn't notice that, almost every time the King came to visit, a crow would fly out of a window, and that crow would not return until well after daybreak.
When the warlock's wife became pregnant, no one thought anything was amiss. Of course, the gossips hoped that the child would not nearly be as powerful a mage as his or her father; one of that kind was more than enough for Camelot. They started looking for possible signs that the baby would be a magic-user; the gossips recalled a bit of news from years previous when the mother of the King's foster-sister was pregnant, vases would shatter unexpectedly and candlesticks would hover. They were relieved when all was normal around the warlock's wife. Perhaps her normal, sensible blood would win out in the end. Of course when the warlock had to leave Camelot as part of his duties as Royal Advisor and Warlock, his wife would always be taken to the palace so she would not have to be alone in her house. Such a fair, loving King would of course take care of the warlock's wife as if she were his sister-in-law.
When the baby was born, the gossips bought the story that the warlock's father, whom no one had ever seen, had been blond.
The King could not have been more attentive to his godson. The gossips approved of this too; the child of the childless King's best friend ought to receive such attention. The boy received the best education his father and godfather could provide—literature, logistics, sciences, elementary medicine, knightly skills. The boy grew in stature and nobility, and the gossips commented that, though the boy was technically low-born, he acted with all the wisdom and dignity of a great Lord far beyond his years. The only thing in which he had no talent was magic, though it was clear to everyone that the warlock did not begrudge his son this. Thus the boy became the shining star of the new Camelot meritocracy at only ten years of age.
A month before the boy turned eleven, the warlock's home caught fire and burnt to the ground. The warlock and his wife had been in it.
No one understood why the warlock was unable to put the fire out or at least escape. No one understood why the warlock's wife didn't manage to get out in time either. The gossips said it was arson, a jealous sorcerer intent on revenge upon the magical defender of Camelot. Little else could explain why the entire house caught fire all over all at once. Only the boy, who had been at the castle studying the stars, survived.
The King went into mourning for the loss of his friend and his friend's wife. The gossips said this was in part for the warlock's son, now the King's ward. No one should have to lose their parents so suddenly and gruesomely at so young an age, just as no one deserved to lose their best friend to something so deliberate. Though the King became no worse a king for the death of his best advisor, he was a soberer man for it. Only his ward, the gossips said, managed to reach the love and joy that the King once had in abundance. Everyone was glad the boy, at least, had lived, one last living reminder of the warlock—or his wife, as the gossips reported that the King regularly would say that the boy looked much like his mother, but for the blond hair the boy had inherited from his father's father.
When the boy was twelve, the King died.
It was not entirely sudden and unexpected. Camelot had been under siege by the force of the Old Ones for some time, and the soldiers on both sides were wearing thin. The soldiers of Camelot managed to destroy the last of the attackers, but it was not without a price. At the last retreat, the sole remaining druid had thrown a single, direct spell, felling the once proud king. No mage in Camelot could reverse the spell. The King commanded with his last breaths that he be placed on the boat going to the Isle of the Blessed; as he was born of magic, so he must die. The gossips didn't quite know what to make of this statement, and theories and guesses ran wild until they were all deemed too silly and disrespectful of their sovereign. His very last request was that his ward, the closest thing the King had to kin, be named Heir to Camelot.
While the whole of Camelot mourned for their King, only the boy could grieve for the man who had once been King.
The boy was crowned King after the body of the King was set adrift on the waters to the Isle of the Blessed. A council of regents and advisors was created, for the young King was still very much a boy. However, it became clear very early on that the boy King was wise beyond his few years, and the gossips said that the regents were often surprised at the wisdom of one so young. In time, the boy became known as the first great King of a nameless dynasty.
King Constantine, the son of the warlock, ruler of all Albion.
In most of the legends, Arthur has no child who he knows is his child—at least of the time of his death. Generally speaking, Arthur's heir is usually Constantine, a cousin of his. However, as there is no mention of any living relatives in the series, I thought I'd take the opportunity.
I haven't written postable fanfiction in what feels like years (is it years? Really?) so any criticism you'd like to throw at me I'd be willing to take. I'm currently experimenting with fairy tales because I'm taking a class in Maerchen next semester.