E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Dieu et mon droit (God and my right). The parole of Richard I. at the battle of Gisors (1198), meaning that he was no vassal of France, but owed his royalty to God alone. As the French were signally beaten, the battle-word was adopted as the royal motto of England.