William Marshal, 1st Earl of Pembroke
Geoffrey II, Duke of Brittany, was another son of Henry II and would have been the next in line to be King but he died on either the 19 or 21 August 1186, at the age of 27.  The more common version is that he was trampled to death in a jousting tournament.  Geoffrey had a son Arthur I, who became the next Duke of Brittany.  Arthur felt that he was also heir to the throne of England. Marshal believed that as a brother to King Richard, and in accordance with Norman custom, John, Geoffrey’s brother, should become the next King.  It was resolved in John’s favor and he became the next King of England.