Arthur I Duke of Brittany
4th Earl of Richmond and Duke of Brittany between 1196 and 1202.
He was the posthumous son of Geoffrey II, Duke of Brittany and Constance, Duchess of Brittany. Geoffrey was a son of Henry II of England, younger than Richard I but older than John. In 1190 Arthur was designated heir to the throne of England and its French territory by his uncle, Richard I, the intent being that Arthur would succeed Richard in preference to Richard's younger brother John. Nothing is recorded of Arthur after his incarceration in Rouen Castle in 1203, and his precise fate is unknown