But now a historian says he has unearthed evidence that add weight to the claims.
When Hitler’s father Alois was born to an unmarried woman, Maria Anna Schicklgruber, in 1836, she refused reveal who his father was and registered him as illegitimate.
In 1930, Hans Frank, Hitler’s lawyer is alleged to have investigated the dictator’s family tree and found evidence that Alois' father, Hitler's grandfather, had been a Jewish man who lived in the same house that Maria worked in.
But the claims are believed to have been covered up. Nikolaus von Preradovich, a German writer, claimed to have proved that there were no Jewish people in the Austrian town where Maria lived in 1936.
Now, speaking to the Mail Online, Dr Leonard Sax, says there is evidence to suggest there was a Jewish community already established in the area just 14 years after Alois Hitler’s birth. Therefore, they may well have been Jewish people living in the area in 1836.
Maria, who was 42 when Alois was born, went on to marry Johann Georg Hiedler and young Alois’ birth certificate was changed when Johann accepted him as his son.
Hitler’s official family tree was published in 1937, at his instruction, and stated that all of the dictator’s ancestors had been Austrian Germans, but the truth may remain elusive.