Cowdray Park Catalogue, London, 1919, p. 6, no. 20, as 'John Sheffield' (in the Buck Hall).
C. Anson, A Catalogue of Pictures and Drawings in the Collection of The Viscount Cowdray, London, 1971, p. 4, no. 15, as 'a Gentleman, said to be the Duke of Buckingham' (in the Buck Hall).
J. Douglas Stewart, Sir Godfrey Kneller and the English Baroque Portrait, Oxford, 1983, p. 136, no. 780, as 'Unknown Man (called 'Duke of Buckinghamshire')' and dated c. 1685.
J. Ingamells, National Portrait Gallery: Later Stuart Portraits 1685-1714, London, 2009, p. 34, under 'Doubtful Portraits'.