From the Conquest in 1066, all English kings down to Henry IV spoke French before English. French was the language of court, the law courts (with Latin) and the new aristocracy which William I created. A linguistic curiosity which remains is the wording of the monarch's assent to a bill from parliament: kings sign Le Roi le veult; queens La Reine le veult. -
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.