“Alas, that ever I bare crown upon my head!” cries Arthur, when he hears about the massacre.  “The Round Table is ended, as I predicted.  We were running on fumes ever since the Grail quest; now we’re done.  Launcelot and his Benwick faction aren’t about to come back, hat in hand, and apologize.  And I can’t forgive the slaughter of more than thirty knights of the Round Table.  There’s no happy ending from this.”

King Arthur speaks to a collection of unspecifed knights, because basically all of his friends and confidantes are either dead, vanished, or in revolt.  The only knights he has left are Sir Gawaine and Sir Mordred.

“That reminds me,” he says, “nobody tell Gawaine about the loss of his so-called surviving brothers.  When he hears Gareth and Gaheris are dead, and that he’s the last of the Orkney faction, he will go night out of his mind.  Mercy Jesu! Why slew he Sir Gareth and Sir Gaheris?  They were good men; they didn’t deserve that.  None of them deserved it.  Except maybe Agravaine, who was pretty much asking for it.  Ah Agravaine, Agravaine, Jesu forgive it thy soul, for thine evil will.”

One of Arthur’s knights takes the initiative, since Arthur has by this point just broken down sobbing, of finding Sir Gawaine and updating him about the massacre.

“I knew it would happen.  Launcelot wouldn’t let her burn.”  Gawaine sighs heavily.  “Gareth and Gaheris are okay, though, right?”  Seriously this is the first thing he asks.

“No, they died,” says the knight, because he forgot what Arthur had just told him.

“Liar!” Gawaine can’t believe it.  “Launcelot wouldn’t kill Gareth!  He and Gareth are buddy-buddy!”

“That’s what people are saying.”  The anonymous knight shrugs.

“Alas, now my joy is gone.”  Gawaine stands there for a moment.  Then he collapses, and lies comatose for hours.  Eventually, he wakes up enough to sob.

Then he runs off to Arthur.  “Uncle Sire!  Gareth and Gaheris are dead!”

“I knooooow!” sobs Arthur, who had just then finally stopped crying.  He and Gawaine embrace one another and start sobbing all over again.

Gawaine wants to have the best funeral ever for his brothers, but Arthur’s already put them in the ground; he did it while Gawaine was unconscious with grief.  “It’s easier this way.”

“I suppose you’re right,” sniffles Gawaine.  “Well, I’m off to murder Sir Launcelot.  Or die in the attempt.  Either way.”

Not so fast, Gawaine!  King Arthur calls for a scribe, and drafts dozens of letters, one for each of his vassals.  He’s earned a whole pile of favors, in his decades as king, and he’s cashing those chips in: every man he can muster will join in a siege on Launcelot’s castle, Joyous Gard.