I've long thought it strange how arnold looks nothing like his dad. Not even a little bit. Children usually strongly resemble their fathers, especially the sons, to the point where just about the only thing short of a paternity test to let a man know if hes been cuckolded is if his children don't look like him. In arnolds case, it is exceedingly obvious because his very prominent facial features are nowhere to be seen in his father.
Recently I was enjoying watching some of arnolds more recent interviews and going over some of his life story, and that was when the other pieces fell into place.
Arnold was frequently victim to abusive behaviour by his father. That in its self is not meaningful, there are plenty of asshole fathers, but what is telling is what Gustav suspected about his son and perhaps why he frequently thought him as less than - Gustav would often lay into his wife and accuse her of having had an affair, believing Arnold could not possibly be his biological son. Arnold also talks about frequently feeling out of place in Austria even at a very young age, "i would think maybe i was the son of some american soldier" and indeed, arnold's facial structure is not typically german. And the year Gustav and Aurelia married coincides with the american occupation of germany.
Of course, this is all speculation and nothing concrete, and in the end who really cares, but my feeling is arnold's mom was a dirty HOOARE and gustav got cuckolded
