There is a semi-mythological genealogy of Breton rulers going back to the fifth century AD (one Cynan Meriadoc was the founder, living about the same time as King Arthur). But the dukes of Brittany cannot be confirmed with any accuracy until the ninth century, when they began to have diplomatic dealings with Charlemagne and his successors.

In the Merovingian period, there were three small Breton kingdoms: Dumnonia, Kernev (Cornouaille) and Broereg. They were unified in the 840s by Nomenoë (son of Frodaldus) , who had been recognized as duke by Louis the Pious, but later led a coalition against an invasion by Charles the Bald and defeated him at Ballon in 845.

Nomenoë seems to have ruled the peninsula from 826 to 851. His son was Erispoë (851-856) also called Harispogus in Carolingian documents; he again defeated the Franks at Jengland in 851. He was the father of a daughter, name now lost, who married a Breton noble called Gurvand, thereafter known as Count of Rennes and Duke of Brittany. Their son Judicaël ruled from 877 to 888. His son's name was also Judicaël, but he is sometimes known by the French name Berenger. Because he ruled from 958 to 970, the genealogy is probably wrong; there must have been one or two generations between the two Judicaëls. But the latter was the father of the very well documented Cynan or Conon I (970-992), "the Crooked" - see below.

During this same period there was a rival ducal family, descended from Salomon, who may have been Nomenoë's brother. He was the father-in-law of Pasquitan of Vannes, who claimed the duchy but left no descendants. He had a brother, however, who successfully claimed the position as Duke Alain I "the Great" (888-907). His daughter married Malhuedoc, count of Poher, and was the mother of Duke Alain II (died 952).

The genealogy is a bit confused at this point, but it appears that Alain II had a son Judicaël, count of Nantes, who married Melisende and had a daughter Judith who was the wife of Alain Cagniart, Count of Cornouaille. This couple was ancestral to another ducal line that eventually merged again with Conon I's descendants. Their son Hoël V of Kernev (died 1084) married Havise, daughter of Alain III (see below). Their son Alain IV 'Fergent' (died 1119) married first Constance, daughter of William the Conqueror, but she had no children; he married second Ermengarde, daughter of Fulk IV of Anjou. Their eldest son was Conon III 'the Fat' (c1071-1148), who married Maud, an illegitimate daughter of Henry I of England. Conon III and Maud had three children: Hoël VI, who died before his father; Constance, who married Geoffroi de Mayenne; and Berthe, considered by some factions to be the heiress to Brittany (and thus the center of much diplomatic maneuvering). She married twice: first, to Alain la Zouche (grandson of Eudes, Count of Penthièvre, see below), by whom she was the mother of Conon IV, declared Duke of Brittany by the English, and who was also Earl of Richmond (see below). Second, Berthe married Eudes II, comte de Porhoët (a grandson of Alain IV), by whom she was the mother of Eudes III (died 1234). He married Léonore de Léon; they had four children, of whom the youngest daughter, Aelis or Alix, married my father's ancestor Guy VI de Mauvoisin, sieur de Rosny.

Conon I "the Crooked" (927-992) married Ermengarde (died p982), a daughter of Geoffrey I, Count of Anjou and Adèle de Vermandois. They had four children, including Judith, who married Duke Richard II of Normandy (and was thus William the Conqueror's paternal grandmother); and Duke Alain III (997-1040), who married Berthe, daughter of Eudes II of Blois and Ermengarde of Auvergne. Their surviving son was Eudes, Count of Penthièvre (999-1079) who was regent of Brittany for his brother Conon II, who was judged incompetent to rule. Eudes married Agnès, daughter of Alain Caignart and Judith of Nantes (see above).

Duke Conon IV (1138-1171), Duke of Brittany and Earl of Richmond, was a pawn in the diplomatic relations of France and England. He married Margaret, daughter of Henry, Earl of Huntington (a member of the Scottish royal family); they were the parents of a daughter, Constance (1161-1201) who was recognized as Duchess of Brittany by Henry II of England, and was married off by him to his own son Geoffrey (1158-1186), who was thereby proclaimed Duke of Brittany jure uxoris. When Geoffrey died his son Arthur, heir to both Brittany and England, was murdered at the orders of the future King John. Constance was then married off to Ranulph, Earl of Chester; they had no children. Eventually allowed to return to France, she married thirdly Guy de Thouars, who now claimed Brittany. They had two children: Alix (called by some Duchess of Brittany; 1201-1222), and Catherine, who married André, sieur de Vitre.

From the time of Alix, the title Duke or Duchess of Brittany belonged to a succession of French noble families, and was out of the English orbit. Alix married Pierre I de Dreux, Duke of Brittany, Count de Penthièvre, Earl of Richmond (died 1250), and produced three children before she died at the age of 21. The eldest was Jean "the Red," Duke of Brittany (1217-1286); the second, Arthur, died young; the third was Yolande de Dreux, who married Hugh XI de Lusignan and was our ancestor through her granddaughter Jeanne, who married Sir Piers de Geneville, Baron de Geneville of Trim and Ludlow Castle, etc, and was the mother of Joan, wife of Roger Mortimer, first Earl of March (see Mortimer). Jean "the Red" married Blanca of Navarre, daughter of Thierry or Theobald, count of Champagne and king of Navarre (see Blois and Navarre) and his wife Agnès de Beaujeu. They had a daughter Alix, who married Jean I de Châtillon, comte de St-Pol (ancestors of Jacquetta of Luxembourg), and a son, Jean II of Brittany (1239-1305) who married Beatrice (1242-1275), daughter of Henry III of England. See Dreux for their numerous descendants; we are descended from this couple through several lines, including Châtillon. The Dreux family eventually ended in the person of Anne, Duchess of Brittany (1477-1514) who married Louis XII and took the titles into the House of Bourbon.

Through Brittany, my mother and father have common ancestors in Conon III 'le Gros' and his wife Maud Plantagenet.