Eleanor, Fair Maid of Brittany
Eleanor the "Fair Maid of Brittany" (c. 1184–1241) was the daughter of Geoffrey Plantagenet and Constance, Duchess of Brittany. Upon the death of King Richard "Lion Heart" of England, a power struggle commenced between her younger brother Arthur and King John of England. At the Battle of Mirabeau, Arthur, Eleanor and Arthur's knights were captured. Eleanor was imprisoned at Corfe Castle. Her brother Arthur was murdered.
Although she had a better claim to throne than the children of John, she was passed over, still captive, in favor of Henry III, John's son, who was crowned in 1216.
Eleanor died in 1241, still a prisoner, forgotten by everyone except her attendants.