He left two sons: his successor, the 16th Duke, and Lord Peter Wimsey, the detective; and one daughter, Lady Mary Wimsey.
His Duchess, née Honoria Lucasta Delagardie, was the daughter of Francis Delagardie, of Bellingham Hall (or Bellingham Manor), Hampshire.
Lord Peter's mother is a strong and sympathetic character, and has attracted much secondary fiction, both by Sayers herself and others. Miss Sayers wrote several pieces of Wimsey fiction, from fragments of chronicles in Old French to the inscription on the 10th Duke's monument. The only piece of this widely published in her lifetime was the "Wimsey Letters" of 1939-40, dealing with their adjustment in wartime, mostly in the voice of the (then) Dowager Duchess.
C.W. Scott-Giles, the herald, worked up Miss Sayers' writings on the Wimseys, including both those privately printed and their own correspondence and discussion on the subject, into the 1977 book listed below.
He began by identifying the Death family above with the Claytons, ancestors of Tarzan. He explains the difference of names by one or both chroniclers using pseudonyms; that the Claytons were North Country earls, and the Deaths appear to be Norfolk squires, related to a baronet, is further obfuscation by our sources.
According to Farmer, Mary Death/Joanne Clayton was Tarzan's great-aunt. She herself had three sons:
This third brother is actually the oldest of the three, having been born before his mother's marriage, and adopted and legitimated by her husband. Before that he was called John Byron Wentworth, being the result of an affair with Byron's grandson, the twelfth Lord Wentworth; he later returned to that name.
Farmer also finds that the Delagardies descend from the Swedish Count Magnus De La Gardie, of terrible memory. His descendants moved to France, were brought to England by Sir Percy Blakeney, the Scarlet Pimpernel. He declares three Delagardie sisters:
In this reconstruction, Count Magnus is from M. R. James's story of that name; Professor Challenger and Lord John Roxton from Sir Arthur Conan Doyle's The Lost World; Rudolf Rassendyll is the hero of The Prisoner of Zenda and Rupert of Hentzau by Anthony Hope. Byron's actual grandson, Byron Noel King-Noel, was in fact Lord Wentworth from 1860 to 1862, between Lady Byron's death and his own, æ. 26; his father, the Earl of Lovelace, survived until 1893.
NOTE -- Some of the material attributed to Farmer in this article was actually researched by other Wold Newton scholars -- in particular, Farmer doesn't mention Mary Death at all in the early versions of the family trees, only citing Joane Clayton, and Magnus Delagardie does not appear at all in the original Farmer texts.