The Once and Future King Book 3, Chapter 18
The next morning, Guenever calls Lancelot and Elaine to her. It turns out that Elaine enchanted herself the night before so that she would appear as Guenever to Lancelot. Guenever does not believe this, even though Elaine admits it, and in a rage throws them both out of the castle. Lancelot runs away in madness, crying. That very morning, he had considered finally leaving with Guenever.