The earliest match is Oscar Wilde and the Black Douglas (1949) by Francis Douglas and Percy Colson, which credits notes taken by Harold Mellor, a wealthy admirer who travelled with Wilde between 1898 and 1900. Beverley Baxter printed the title’s wording in The Sketch that April, from a collection Colson sent him, some of it Colson’s own. Quote Investigator calls Wilde’s authorship plausible but unproven.