Bertha of Cornouaille (fl. 1125–56), also known as Bertha of Brittany (Breton: Berthe Breizh), was the Duchess of Brittany between 1148 until her death and Dowager Countess of Richmond. Bertha was the elder daughter of Conan III of Brittany by Maude, the illegitimate daughter of King Henry I of England.[1] She was the last member of the Breton house of Cornouaille to reign over Brittany.