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.
Bertha was the daughter of Duke Conan III of Brittany.
On his deathbed, Conan III renounced Bertha's brother Hoel as heir[2] and designated Bertha as his heiress, Duchess of Brittany.
[3] In her first marriage, by 1138, Bertha was married to Alan the Black.