The article studies the history of the use of the French language as the language of international diplomacy. Despite the traditional point of view according to which this period started in 1714, the first international diplomatic document to be written in French was, in actual fact, the treaty of the devolution of the French crown to the King of England that was signed by the King of England, Edward III and the King of Navarra, Charles II the Angry 1 August 1351. The authors explain whu this fact has been ignored by the official French historiography.