I would love to know the truth, whatever it may be. I really don't understand the catty insulting replies made to my post. I was hoping someone on here may be able to point me in a research direction, but I suppose I came to the wrong place.
You came very much to the correct place. You are about the two thousandth person to come here with family claims of being descended from an illegitimate child of a Russian Emperor. The "catty" results are because of the familiarity and (to the well educated on the subject) ridiculousness of the allegations.
There is simply no "research" direction for you. Alexander III did not have a female doctor, period. He had no doctor "Prokofieff" period. "White Russians" were SUPPORTERS of the Emperor Nicholas II and didn't "rebel" against the regime. "White Russians" were not imprisoned in Peter and Paul for "crimes against the Emperor" (by the way, Nicholas II was not actually "Czar" he was "Emperor"). Thus your story has a glaring contradiction.
Now, as a member of the Imperial Aeoronautic Club and Officer he might have been held there during the Revolution by the early Kerensky government. The Fortress Courtyards are rather drab, slab block affairs, not Gothic Arches, however there is a "Gothic Revival Chapel" in the Fortress and the drawing might be of the Chapel windows, there is some strong similarity.
My Russian isn't good enough to exactly translate the notebook's label, but it doesn't appear to be "prison issued" rather some sort of school theme book. I have a similar book belonging to one of Grand Duchess Xenia's sons, which is also filled with doodles and drawings and hand drawn cartoons, which tells me young men in that period often used those school notebooks in that manner.
Many emigré families often embellished their histories or outright lied (My own uncle used to regale me with tales of his service in France in WWI and even gave me the Croix de Guerre he carried as proof, after he died, I asked my Grandmother, his sister, about it. She laughed and said "Charles was rejected from the Army for his eyesight. He won that in a card game years later....he never fought in France....")