Born in the Austrian village of Spital, Weitra, Waldviertel, her father was Johann Baptist Pölzl and her mother was Johanna Hiedler. Either Johanna Hiedler's father Johann Nepomuk Hiedler or his brother Johann Georg Hiedler (who is presumed and accepted as the father) was the biological father of Klara Hiedler's husband, Alois Hitler, Sr.. Therefore, Klara and Alois were most likely first cousins once removed.*
I am a little bit puzzled by the statement that Klara and Alois Hitler were "first cousins once removed". From the text it stemms that Alois and Klara were uncle and niece (The godfather of Klara Hitler was at the same time the father of Alois). But the term "cousins once removed" indicates a different sort of the relationship between AH's parents. Or does it not?