The fact is that, for a long time, British kings considered themselves kings of France as well - and even believed that France was the senior kingdom. The language they spoke reflected that attitude.

That said, as a Frenchman who has to speak English every day, I can assure you that English has long since become its own thing!

They spoke French because they were Normans and married mostly with the continental aristocracy.

Their claim to the French throne was based on the rules of succession and an argument over them (arising from those intertwinned lineages).

An interesting fact is that King Richard I (Sean Connery in Robin Hood with Kevin Costner)'s mother was from South West France and he grew up there, and so he spoke French and Occitan but not really English.

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