John, King of England:

During John's early years, Henry attempted to resolve the question of his succession. Henry the Young King had been crowned King of England in 1170, but was not given any formal powers by his father; he was also promised Normandy and Anjou as part of his future inheritance. Richard was to be appointed the Count of Poitou with control of Aquitaine, whilst Geoffrey was to become the Duke of Brittany. At this time it seemed unlikely that John would ever inherit substantial lands, and he was jokingly nicknamed "Lackland" by his father.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Who became the Duke of Brittany?
Geoffrey