He had an elder sister, Rosamond Patricia Susan Anne Cornwallis (15 May 1918 – 3 September 1960).
During World War II, Lord Cornwallis served with the Coldstream Guards between 1940 – 1944 when he was invalided out of the army.
His specialised collections of Australia, Gambia, Gibraltar, and Malta stamps were sold in 2011.
He married, secondly, Agnes Jean Russell (née Landale), daughter of Captain Henderson Russell Landale, on 1 June 1951 with whom he had four children: Patrick Wykeham David Cornwallis (b.
27 July 1958), and Susan Patricia Rose Crolla (née Cornwallis) (b.