Margawse comes back into the picture at this point. You may have forgotten her: she’s Arthur’s older half-sister, child of Igraine and Igraine’s first husband Gorlas. Uther married her off to Lot before he died. Now Margqwse is the Queen of the Orkneys, whose husband does not appreciate her. She sends word to Arthur that she’d like to come visit, as Queen of the Orkneys, since her husband is off fighting Saracens and there’s no reason Margawse and Arthur can’t get along.
Neither of them are aware that they have the same mother, Malory tells us, and that kind of disclaimer only makes sense if… yes.
Long story short, Mordred is raised out in the Orkneys along with Margawse’s other four children, his half-siblings since their father is Lot and his father is Arthur. That’s great. We’re a pretty small fraction of the way through the story and already Arthur has sired two illegitimate children, one with his half-sister.
Anyway, sometime after fathering Mordred, Arthur has a dream, in which an army of monsters invades England, and Arthur fights them and just barely wins. This bugs Arthur, I guess he thinks that if he battles monsters he should win easily, so to cheer himself up he decides to go hunting.
Arthur moodily hunts for a while, almost bags a deer, doesn’t, moodily changes horses, moodily hunts some more, then decides to call it a day and waters his horse at a fountain and mulls over the existential angst of being King Arthur. While he’s doing this, he hears what he thinks is a pack of thirty or so hounds, but no, it’s the questing beast. The questing beast sounds like that, apparently, and it shows up and drinks from the fountain, then leaves.
“Peculiar,” thinks Arthur. Then he lays out for a quick nap.
However then a knight walks up and pokes him with his foot and says “excuse me stranger, dude, wake up. I’m looking for a beast which cannot be described except to say that it sounds like thirty hounds, have you seen him?”
And Arthur says, “yeah, it went that way.”
“Terrific!” says the knight. “Now if only I had a horse.”
At this point one of Arthur’s servants shows up with another horse. “You wanted a spare horse, your majesty?”
Arthur shakes his head, because he already got his second horse like two hours ago; there’s been some kind of mixup in the stables.
“Since you aren’t using this horse,” says the strange knight, whose name is Pellinore. “Hint, hint.”
“What? Am I getting punk’d?” asks Arthur. “Am I dreaming? Are monsters about to appear? Has a mystery play sprung up around me? What is happening?”
Pellinore explains that he’s on a quest to catch the questing beast, as if this answered all Arthur’s questions.
“Okay, I’ll play along,” says Arthur. If I was Arthur I’d be better-looking. I’d also suspect I was in some kind of dream or allegory or crazy Merlin prank situation.
Anyway, Arthur wants to play along. “Yo, Pellinore,” he says. “How about you stop questing after this ‘questing beast,’ and I’ll go quest after it for, I dunno, a year? Or until I catch it.”
“Arthur you ignoramus,” says Pellinore, “only I can catch it. Or one of my sons. Or a nephew, or my father, or an uncle, if he’s a paternal uncle. You get what I’m saying; I’m a sexist jackass but who isn’t these days?”
While Arthur mulls this over, Pellinore steals his horse.
“My horse now,” says Pellinore. “I need it to catch the questing beast. The score is one horse Pellinore, zero horses Arthur!”
Arthur mumbles something about Pellinore better being ready to fight him for it, to which Pellinore laughs and says he’ll be there, right there, at this fountain, any time Arthur wants to fight. Any time at all! Pellinore isn’t going anywhere! Then Pellinore rides off.
Arthur needs to lie down after all that.