In 1199, when Richard the Lionheart died, there were two possible claimants to the throne of England -- his younger brother John, and his nephew Arthur. John was a bit over 30 years old; Arthur was about 12. John, the youngest surviving son of Henry II, was by Norman law the rightful heir. Arthur, the eldest son of Geoffrey, John's older brother, was by the laws of Brittany, the rightful heir. Also, John was in England and Arthur was in Brittany. Also, John was the person who was, well, John. Ruthless, is what he was.  You can guess who it is who won, especially since you've already heard of King John and Arthur of Brittany sort of fell through the cracks of history. Except that the French really like him, and wrote a bunch of plays, and the Victorians loved him bunches because he was so pathetic. Michelle explains all that.