He is the eldest surviving son of the 11th Duke of Marlborough and his first wife, Susan Mary Hornby. As a member of the Spencer family, he is a distant relative of the war-time Conservative Prime Minister Sir Winston Churchill and of Diana, Princess of Wales, born Lady Diana Spencer. He is also a stepbrother of the late Christina Onassis, who was the step daughter of Jacqueline Kennedy Onassis, who was once married to U.S. President John F. Kennedy, by the second marriage of his father with Athina Livanos.