Constance, Duchess of Brittany

Constance, Duchess of Brittany (died 1201) was the wife of King John's older brother, Geoffrey. Her father was Conon le Petit, Duke of Brittany and Earl of Richmond in Yorkshire. Her mother was Margaret (also known as Ada), daughter of Henry Earl of Huntington (who was the son of David I, King of Scots). Her third husand was Guy Viscount of Thours.

Constance is the mother of Arthur of Brittany, the young boy apparently killed on orders of King John. She has several very eloquent speeches on grief and death in Shakespeare's play King John.