Answer
Alois Hitler, the father of Adolf Hitler, originally bore the surname Schicklgruber. His paternal grandfather was Johann Georg Hiedler, who had an illegitimate son, Alois, with Maria Anna Schicklgruber. Johann Georg later married Maria Anna, but Alois retained his mother's surname until he was 39 years old when he officially changed it to Hitler, possibly to avoid the stigma associated with illegitimacy.