The Once and Future King Book 3, Chapter 4
Lancelot is very upset that he is not the closest to Arthur. On his way to the castle, he comes upon a knight dressed in black. They spar and Lancelot wins. The knight turns out to be Arthur. They are very happy to see each other, and Arthur gives him news: Gawaine killed a woman in a rage, and Pellinore killed King Lot by accident in a tournament, and the Round Table was going fairly well. When he meets Guenever, Lancelot feels nothing but anger and jealousy. Lancelot stays at the castle, and Guenever goes out of her way to be nice to him. She goes with him when he trains his hawk, and tries to help him with his supplies, but he gets angry with her. When he sees she is hurt, for the first time he realizes she is human: "She was pretty Jenny, who could think and feel." Book 3, Chapter 4, pg. 348