JEAN de Bretagne, son of PIERRE I Duke of Brittany & his first wife Alix de Thouars Dss of Brittany ([1217/18]-Château de l'Isle, Férel, Morbihan 8 Oct 1286, bur Prières, église abbatiale de Notre Dame). The Chronicon Ruyensis Cœnobii records the birth in 1217 of "Johannes filius Petri Comitis et Aelidis Comitissæ Britanniæ"[368]. The Chronicon Britannicum records the birth in 1218 of "Johannes, filius Petri Ducis Britanniæ"[369]. On his marriage his father-in-law declared Jean as his heir in Navarre, even if he subsequently had a male heir. After his majority, his father resigned the duchy and Jean swore allegiance to Louis IX King of France in Paris 16 Nov 1237 as JEAN I "le Roux" Duke of Brittany, Seigneur de Pontarcy, de Brie-Comte-Robert et de la Fère-en-Tardenois. Seigneur de Muzillac [1250]. He renounced his rights to Navarre for an annuity of 3,000 livres, by agreement 1254. Châtelain de Dinan 1264-1265. Seigneur de Hédé, de Hennedon-le-Viel, de Léon et de la Roche-Derrien 1265. Vicomte de Gourin [1265]. Henry III King of England restored him as Earl of Richmond at Woodstock 15 Jul 1268, but he immediately surrendered the earldom to his son. He accompanied Louis IX King of France on his second Crusade in 1270. Comte de Penthièvre, Seigneur de Lavaux 1272. Comte de Léon 1276. The Chronicon Britannicum records the death "Id Oct" 1286 of “Joannes comes Britanniæ fundator abbatiæ de Precibus” and the succession of “Joannes filius eius”[370].
m (contract Château-Thierry, Aisne 16 Jan 1236) Infanta doña BLANCA de Navarra, daughter of TEOBALDO I King of Navarre [THIBAUT IV Comte de Champagne] & his second wife Agnès de Beaujeu (1226-château de Hédé, Ille-et-Vilaine 11/12 Aug 1283, bur Hennebont, Morbihan, Abbaye cistercienne de Notre dame de la Joie). The Chronicle of Alberic de Trois-Fontaines records that "Agnes comitissa Campanie" left an only daughter but does not name her[371]. The marriage contract between “P. dux Britannie comes Richerimontis…Johanni de Britannia filio nostro” and “Theobaldus…rex Navarre, Campanie et Brie comes palatinus…filiam suam domiscellam Blancham” is dated 16 Jan 1236[372]. She founded the Abbaye de la Joie near Hennebont [1270], where she was later buried. The Chronicon Britannicum records the death "pridie Id Aug" 1273 (presumably error for 1283) of “domina Blancha ducissa Britanniæ” and her burial “apud Henbond”[373]. The necrology of the Abbaye des Clairets records the death "IV Id Sep" of "Blancha comitissa Britannie"[374].
Duke Jean I & his wife had eight children