Now, originally, King Mark killed Sir Tristram and Le Bel Isode later committed suicide, but in this story, Sir Lancelot finds out about King Mark's plot to kill Sir Tristram, so Sir Lancelot kills King Mark before he can kill his best friend, and that's how Sir Tristram became the King of Lyonesse, after his father Meliodas, and Le Bel Isode is now the Queen of Lyonesse, and the wife of Sir Tristram.