There is really no mystery here. Grand Duke Paul has a number of great grandchildren, including the grandchildren of Lennart, Count Bernadotte, and the grandchildren of Grand Duke Dmitri. (And also for the record, great grand children through Princess Irene Paley). However, by process of elimination, I believe he is referring to HSH Prince Michael Pavlovich Ilyinsky, a very fine gentleman with great interest in his family history. Who does post here on occasion.