Page "Duchy of Brittany" Paragraph 53

John III's brother Guy de Penthièvre predeceases him and leaves his daughter, Joanna of Penthièvre as a claimant to the Ducal Crown.

In 1337 Joan, Duchess of Brittany married Charles de Blois ( Charles I, Duke of Brittany ) but war ensues upon their assumption of the titles Duke and Duchess of Brittany due to the opposition of John IV who does not cede his own rights.

The Breton War of Succession was fought from 1341 to 1364 between the House of Blois and the House of Montfort.

John of Montfort emerged victorious with substantial help from English allies and became John IV, Duke of Brittany reigning for a short period.

Joan and Charles were allowed to keep Penthièvre, and Joan retained the title Duchess of Brittany for life.

The Houses of Penthièvre and Montfort were united in their opposition of Charles V of France who took the opportunity of this Civil War to attempt the annexation of Brittany to the French crown.

This line of the Blois-Penthièvre family maintained close ties to the successive kings of France and through the French crown the family were often present in Brittany in some oversight capacity.

Under the Treaties of Guerande semi-Salic succession was agreed under which, if the reigning member of the House of Montfort died without legitimate male issue, the eldest direct legitimate male descendant of Joanna of Penthièvre would inherit the Ducal crown of Brittany.

The victory of the House of Montfort strengthened the position of England in Brittany.

The conflicts between the House of Montfort and the House of Penthièvre continued into the 15th century.

One of the effects of the Breton War of Succession was to intensify the rivalries between England and France with Brittany as the contested prize.