Joan de Ferrers Peerage person ID=42693 (1228–1267) Parents William de Ferrers, 5th Earl of Derby Sibyl Marshal Children Isabel Aguillon Sir John de Mohun Siblings Alianore de Ferrers Elizabeth Ferrers Robert de Ferrers, 6th Earl of Derby Isabel Ferrers Agatha Ferrers Sibyl de Ferrers William Ferrers Agnes de Ferrers Maud Ferrers Joan de Ferrers Agnes Ferrers Partners Sir Robert Aguillon John de Mohun