 His mother, Rosalie Eugenia Stier (1778–1821), was the daughter of a wealthy Belgian aristocrat, Baron Henri Joseph Stier (1743–1821) and his wife Marie Louise Peeters.His father, George Calvert (1768–1838), was the son of Benedict Swingate Calvert – a natural son of Charles Calvert, 5th Baron Baltimore – and his wife Elizabeth Calvert (1731–1788).George Calvert was the Calverts' eldest son.