Paternity of Herman op den Graeff

The highly respected researcher William Addams Reitwiesner considered that the idea that Herman was a son of Johann Wilhelm, Duke of Julich Cleve and Berg (1562-1609) was fanciful and unlikely.

See http://www.wargs.com/family/ancestry.html#Note3208

Has anyone any confirmation or better information?

No comment in two and a half years? Here's the Familypedia page for study:
http://familypedia.wikia.com/wiki/Herman_op_den_Graeff_%281585-1642%29

Robin:
Do you think it's time to remove/replace the parental tie as there is no sourcing to show that Hermann Isaac is
the son of Johann Wilhelm, count of Jülich & Cleves and Anna van Aldekerk ?

I think it might be time as it is confusing as there are sites that say John WIlliam died without any kids and if you trying to do research on family and come across this saying this Herman guy is his kid then you may not know what to do..

Johann Wilhelm had no children. He had a nerve disease and became catatonic. A lot of doctors, healer and exorcists are not able to heal him.
I think an aristocratic family was good for Hermann Isaacs career, Someone create it later.

In addition to adding a specific curator note to Hermann, I've also added one to the purported father Johann Wilhelm, count of Jülich & Cleves to hopefully minimize this from re-occurring.