William de Ferrers, 3rd Earl of Derby English Earl (1200–1190) Parents Margaret Ferrers, Countess of Derby Robert de Ferrers, 2nd Earl of Derby Children William de Ferrers, 4th Earl of Derby Millicent de Ferrers Petronell de Ferrers Walkelin de Derby Agatha de Ferrers Siblings Walkelin de Derby Partners Sibyl de Braose