Complex sentence: The Lady Sophia Louise Sydney Topley (née Cavendish; born 18 March 1957) is the third child and second daughter of the 11th Duke of Devonshire and his wife, Deborah Mitford, and the younger sister of the (present) 12th Duke.
Split into simpler sentences: The Lady Sophia Louise Sydney Topley (née Cavendish; born 18 March 1957) is the third child and second daughter of the 11th Duke of Devonshire and his wife, Deborah Mitford. She is the younger sister of the (present) 12th Duke.