However Middleton had a broader mandate for the Sports Control Board and it wasn't until May 1919 when the rugby carnival had completed, and the boxing and athletics events had concluded that Middleton himself joined the AIF Rowing Section as a competitor. Middleton was in the six seat of the AIF #1 eight by the time of the Marlowe Victory Regatta on 21 June 1919 and then for the Henley Peace Regatta in July 1919 Middleton was again at six, balancing up the power from his old New South Wales King's Cup and Australian Olympic team-mate Henry Hauenstein in the five seat. The AIF#1 crew won the cup for eight-oared boats, which was presented by King George V; and, in time, from this, the ""King's Cup"" has become the trophy presented to the winning men's eight at the annual Australian Rowing Championships. Middleton had met Marion Streatfield, a nurse when at the war's end having commenced his work with the Sports Control Board, he was admitted to the 10th British Red Cross Hospital in Le Treport, France suffering from catarrhal jaundice. They were married in September 1921 in London and lived in Iverna-Gardens, South Kensington. They had one son John Peter who served as a second lieutenant with the 12th Royal Lancers in WWII in Italy from 1944. Syd Middleton died suddenly on 2 September 1945.