I was talking about the original French annexation of Brittany, not the WWII invasion: Once British, it became an independent Duchy, before forced integration with France.
“The independent sovereign nature of the Duchy began to come to an end upon the death of Francis II in 1488. The Duchy was inherited by his daughter, Anne, but King Charles VIII of France had her existing marriage annulled and then married her himself. As a result, the King of France acquired the title of Duke of Brittany — jure uxoris. The Ducal crown became united with the French crown in 1532 through a vote of the Estates of Brittany.
Following the French Revolution, and as a result of the various republican forms of French government since 1792, the duchy was replaced by the French system of départements (or Departments) which continues under the Fifth Republic of France. In modern times the departments have also joined into administrative regions although the administrative region of Brittany does not encompass the entirety of the medieval duchy.”