And if you are interested in the puzzles around Hitler's origins, this book may be useful:
Mayerling ohne Mythos. Ein Tatsachenbericht. Kremayr & Scheriau, Wien 1968. (Lizenzausgabe 1984 neu bearbeitet von Margot Judtmann, OBV).
Yes, it is in German. One commentator on the web referred to it thus:
———
So far, the best evidence I've seen about the true feelings of Rudolph for Mary Vetsera were in Fritz Judtmann's book where he said he saw telegrams from Rudolph to Mary and it was clear that although Rudolph was extremely polite and careful in his wording, he was truly trying to free himself of their relationship.
———
Sp for anyone thinking that Mary Vetsera changed her name to Klara Hitler or that she was impregnated by Prince Philipp Saxe-Coburg-Gotha (who was at Mayerling during the deaths if they really were deaths) this account of the telegrams leaves both possibilities quite open.
And then there is Carl Heinrich Hoffman of Des Moines IA and maybe Kirksville MO, an osteopath who may be Rudolf von Habsburg hiding out. The main account is found at ATSU.edu in old Osteopathic journals from 1903.
The question of who is related to who is not easy to bottom out.