Joan, Duchess of Brittany

Joan of Penthièvre
Tomb of Jeanne de Penthièvre, duchess of Brittany
Duchess of Brittany
Reign	30 April 1341 –1365 (disputed suo jure) 1365–10 September 1384 (titular)
Predecessor	John III
Successor	John IV
Born	1319
Died	10 September 1384 (aged 65) Guingamp
Burial	church of the Friars Minor of Guingamp.
Spouse	Charles I
Issue	John I of Blois-Châtillon Guy Henry Marie, Lady of Guise Marguerite, Countess of Angoulême
House	House of Dreux
Father	Guy, Count of Penthièvre
Mother	Jeanne d'Avaugour
Religion	Roman Catholicism

Joan of Penthièvre or Joan the Lame (in French Jeanne de Penthièvre, Jeanne la Boiteuse) (c.1319 – 10 September 1384) reigned as Duchess of Brittany suo jure together with her husband Charles of Blois between 1341 and 1364. Her ducal claims were contested by the House of Montfort, which prevailed only after an extensive civil war, the War of the Breton Succession. After the war, Joan remained titular Duchess of Brittany to her death. She was Countess of Penthièvre in her own right throughout her life.

Joan was the only daughter of Guy, Count of Penthièvre, the brother of Duke John III, and Jeanne d'Avaugour. Through her father she became Countess of Penthièvre in her own right, and established her ducal claims.

Joan was one of the protagonists of the War of the Breton Succession. The issue of succession to the ducal crown would involve the issue of whether a child could, regardless of gender, claim the right of "representation" of a deceased parent — in which case Joan would inherit her father's rights as the second brother of the late duke — or whether the next eldest male heir in a partially collineal line outranked all others. In the Breton succession, the collateral claimant was Joan's half-uncle John of Montfort, born from the second marriage of Duke Arthur II to Yolande of Dreux. John III had been alienated from Yolande, his stepmother, and sought to prevent his half-brother from succeeding him, including an abortive attempt to annul his father's second marriage and so render his half-siblings illegitimate.

In 1337, Joan married Charles of Blois in Paris. In 1341, on the death of John III, the couple assumed the rule of the duchy of Brittany, Charles having been granted permission to perform homage by King Philip VI by the arrêt of Conflans on 7 September 1341. They appeared to be supported by most of the local nobility and administration. However, John of Montfort did not agree to let go of his own rights, and war ensued.