UPDATE, from Peter Duby “This painting is by my father, Georges Marcel Theophile Duby (1911-1997), not by the French medieval historian with the similar name, Georges Michel Claude Duby. I would have recognized the portrait by style and technique alone – without the, to me, familiar signature. My father was an artist, and I would have thought that this portrait was done in 1945 - shortly after his return from military service with the South African Air Force. I don’t know with certainty who is portrayed, but it is probably one of his airforce chums, my guess his Capt. Louis Gordon (of 12 Squadron SAAF, awarded the Distinguished Flying Cross in 1942 and remained in the SAAF after the war).
My father went on to work for Satour and continued to paint into his eighties, producing a portrait of Jan Smuts that hangs in the RAF College at Cranwell and another of Chris Banard. He was responsible for the design of the 1966 issue of Rand banknotes and for a number of years did the layout of Lantern magazine for the Foundation for Education, Science and Technology. In the 1970s he co-wrote Our Art with Heine Toerien. He also served for a number of years as chairman of the Pretoria branch of the South African Association of Arts, exhibiting frequently at their gallery off Church Square in Pretoria.”
Many Thanks to Peter Duby for the information!