The selections from Morte Darthur which are summarized in the following paragraphs tells the story of the how King Arthur found out of Queen Guinevere and Sir Lancelot''s betrayal and of the outcome of this discovery. They also tell one version of the way Arthur died and brought to burial.
Two Knights of the Round Table, Agrvain and Mordred, have a secret grudge against Lancelot, the most accomplished of Arthur''s knights. Despite Sir Gawain''s (Arthur''s nephew and a Knight himself) request they tell Arthur about Lancelot and Guinevere affair. To supply the proof to the suspicious Arthur, the two Knights and their supporters gather outside the queen bedroom and demand that Lancelot, who is there with Guinevere, turn himself into them. Lancelot kills the knights and flees the castle.
Lancelot rescues Guinevere right before her execution. In the mayhem he kills Sir Gareth, Gawain''s beloved brother. Grief-stricken Gawain takes swears to avenge his brother''s death. Lancelot recruits Arthur to his help and the two of them along with noble men from all across the kingdom sets out for Lancelot''s castle.
We meet Arthur again after a treaty was made between Lancelot and him. Now Mordred is trying to overthrow Arthur. On the night of the battle between them, Arthur is warned in a dream not to fight. Due to unfortunate chain of events the battle does take place. Arthur kills Mordred, but suffers a fatal injury. Still alive, he is led by his only surviving knight to the river, where his sister awaits him. He was probably brought to burial by her, but no one can verify it with absolute certainty.