The Once and Future King Book 3, Chapter 37
Before Arthur's reign, someone accusing the Queen of anything would be killed immediately, but now, because of the new justice, she could be burned if found guilty. Lancelot comes to the rescue at the last moment. He had gone to God because he felt in a very personal way that he loved God more than he loved Guenever, and that maybe God even needed him more. He returns to Guenever now because he does still love her, and she is in desperate need of him. He defeats the knight who has accused her, and Arthur thanks him in front of everyone, as Guenever cries behind him.