Original seals, vintage postmarks, and authentic signature have left little doubt the letters are genuine.
When contacted by a woman claiming to have unearthed letters written by Adolf Hitler's father in her attic, Austrian historian Roman Sandgruber was naturally suspicious.
"At first, I was rather skeptical: very little is known about the youth of the Führer and even less about his father," said the specialist, who expected to come across a discovery once again.
However, the correspondence quickly proved to be authentic: original seals, the vintage postmarks, the authentic signature — left him with little doubt the letters were genuine.
The letters were written during the Austro-Hungarian Empire, for the attention of a certain Josef Radlegger concerning the latter’s sale of a farmhouse in the village of Hafeld to Alois in 1895, when Adolf was six years old.
Though Alois was known to be a "very tyrannical head of the family," Sandgruber said the letters also offer an occasional glimpse at congeniality in his home life.
And while Alois is known to have made anti-Semitic statements when he himself dabbled in politics later in life, Sandgruber is wary of making too many direct connections between the father’s politics and those of his son.
They also give a different image of his mother, Klara, portrayed by Adolf Hitler as a quiet "little housewife" in his book Mein Kampf.
"My wife likes to be active and has a certain enthusiasm as well as a good understanding of economics", writes Alois Hitler to his business partner.
All this would never have come to light without ... thermal insulation work! A few years ago, an Austrian woman, far from suspecting what was lying under her roof, decided to insulate the attic floor and empty the attic for that.