She was the illegitimate daughter of Bonnie Prince Charlie. Her Wikipedia article is here. "...Her mother was Clementina Walkinshaw, who was mistress to the Prince from 1752 until 1760. After years of abuse, Clementina left him, taking Charlotte with her. Charlotte spent most of her life in French convents, estranged from a father who refused to make any provision for her. Unable to marry, she herself became a mistress with illegitimate children, taking Ferdinand de Rohan, Archbishop of Bordeaux, as her lover..."
From Wikimedia; paint crack flaws fixed with Photoshop.