Good guess. It happened about a thousand years ago. In 1066, England was invaded and then occupied by an army of Norman, Breton, and French soldiers led by Duke William II of Normandy, later called William the Conqueror. The occupation lasted for a long time, sufficiently so that the newly introduced language, Old French, took root, the English aristocracy was replaced, a lot of continentals settled in England, and intermarriage became common. And so Old French language and customs intermingled with Anglo Saxon.
That is why English is such a rich language, too, why it has such a large vocabulary, and there is often more than one word for the same thing -- both Anglo Saxon and Old French roots have persisted.
Very convenient for students. ;)
And students should be very grateful for the ensuing simplification of English verb conjugation, the rejection of the ideas of a grammatical gender for every noun, and the requirement to alter adjectives to "agree" with these unnecessary, arbritary genders - all so that the different communities could communicate more easily with each other, or so one theory suggests.