Dreux

The House of Dreux was a Capetian cadet branch, founded when Robert I, younger son of Louis VI, received the County of Dreux as his appanage. Long minor nobles, the family's fortunes changed in 1212, when Peter of Dreux married Alix, heiress of Brittany, and ruled it as duke; the French court recognised Brittany as a lay peerage and duchy in 1297.

In 1337 John III held Brittany while the senior Dreux line, extinct in 1345, still kept its county. John III's death in 1341 opened the War of the Breton Succession: Joan of Pentievre and her husband Charles of Blois, backed by Philip VI, fought John of Montfort, backed by Edward III.

Montfort died at the siege of Quimper in 1345, Charles of Blois fell at Auray in 1364, and the Treaty of Guerande gave the duchy to the Montfort line. When its last male duke, Francis II, died, Brittany passed to his daughter Anne, who married two successive French kings.