Prince Pierre Troubetzkoy, (1864 - 1936)
Photograph by Frances ["Fannie"] Benjamin Johnston, (1864-1952), Library of Congress archive.

Rabbit Meets Hat supplied this image of the Prince (see yesterday's post); "magnificent speciman of manhood" indeed.  Further investigation into the American photographer Fannie Johnston produced this next photograph, also in the LOC archives, of the Prince's studio at 15 West 67th Street:

  

which looks to me remarkably like the cooperative unit in the same building currently on the market [Here], or at least one in the same building, and on this site you can also see the early 20th century Deco-Gothic stone street entrance.

And further, just to prove that Everything is Connected, the Metropolitan has in its Alfred Stieglitz Collection a photograph, taken by the Prince of his wife Amelie Rives, the Princess Troubetzkoy, and printed by Alvin Langdon Coburn in 1904.