Hot off the press, it looks like the newer book has already inspired the discovery of this mystery person's identity. Kenneth Hard, grandson of F.G. Bourne, tells us that the super sleuth is his son, Gary S. Hard. In his research, Gary found a Dec. 4, 1926 New York Times article that reports about a "Henry D. Bradley of New York, who attended" Marjorie Bourne's marriage ceremony to Alexander D. Thayer in the Episcopal Church of the Messiah, "near Norristown" i.e., Gwynedd Valley PA.
As further evidence, Gary found a Dec. 16, 1973 New York Times article reporting the death of this H.D.B. It states: "Henry D. Bradley, president and retired publisher of the St. Joseph New Press and Gazette and a former director of the Associated Press died [Dec. 14, 1973] ... He was 80 years old." Included in an impressive list of credentials, the article states: "He was general manager of the Norristown (Pa.) Times Herald from 1924 to 1926".
This blog is the first outlet to reveal this exclusive breaking news to the world, which apparently has many afficiandos of the mysterious Dark Island lore in the Thousand Islands. Great work Gary!