Just saw this and since it's an area of interest....
The "well known Russian author" involved with The Scandalous Mrs. Blackford was Alexandre Tarsaidze. The book is a novel, as is Prince Michael of Greece's book. The book is, though, based heavily on Henrietta's own 1874 memoirs-the authors correctly state that few copies survived and many were seized and censored in Paris and in Brussels by authorities at the request of the Russian Government anxious to conceal the scandal over her relationship with Nicholas Konstantinovich. That said, almost everything in the book about Henrietta before she sets foot in Russia is fiction-Penny Wilson and myself (with the assistance of several generous and skilled researchers) have conducted extensive research on her life in Russia and in America and even obtained her brother-in-law's personal copy of her memoirs with her annotations. There is a huge amount of material-love letters, reports on Henrietta, etc., in Russia that has filled out the story quite a bit, but I'd only consider the sections dealing with her relationship with Nicholas Konstantinovich to be close to the truth-anything else is best read as fiction.