From Reinhard Heydrich since I don't have my books handy:
"Since Heydrich's death, historical evidence has come to light that Heydrich may very well have had a Jewish grandparent and that this fact was known to high Nazi leaders including Hitler and Himmler. Under the Nuremberg Laws, Heydrich would have been classified as "a person of mixed Jewish blood in the second degree", meaning he had one pure German and one half Jewish parent. Heydrich would not have been subject to anti-Semitic laws, but would have been expelled from the SS as being non-Aryan.
"The most compelling evidence of Heydrich's Jewish ancestry is the testimony of Walter Schellenberg who stated, in the 1950s, that Heinrich Himmler had held a private meeting with Heydrich in 1935, after learning that one of Heydrich's relatives had held the surname of "Süss", a common Jewish name. According to Schellenberg, Heydrich admitted that one of his grandparents was Jewish and Himmler had reportedly informed Hitler. Hitler, however, stated Heydrich was a special case since "his Aryan blood far suppressed his Jewish heritage". Shortly thereafter, Gestapo personnel were dispatched to Halle, where Heydrich had been born, to erase certain records of Heydrich's past. Rumours arose that this included the destruction of tombstones, but this is unconfirmed.
"It was not long before other Nazis had heard insinuations that Heydrich might have had a Jewish relative in his background. Dr. Achim Gercke, the Nazi Party's leading genealogist, was commissioned by Gregor Strasser after a Nazi official, Rudolf Jordan, revealed the grandfather to Party Headquarters in 1932. Gercke claimed research that not only was the Süss in question, a locksmith, not even a Jew, but that he wasn't even Heydrich's genetic grandfather, whose name was Reinhold Heydrich. Also of note is that the investigation was concluded in the summer of 1932, rather than 1935.
"The accuracy of both Schellenberg's and Gercke's testimonies are today still debated among historians. Some works on Heydrich have thus far dispelled the story as a rumour. The assertion is also routinely denied by neo-Nazis. However, it is widely accepted that Heydrich did believe the claims at least enough to try and make up for it by even greater devotion to the Nazi cause."
Well, old Reinhard's remains have been run and rerun through so many worms that the truth is hard to find...
Interestingly, to me, the only top Nazi who may well have been half Jewish [under Nazi theory], and who is never accused of it, is Hermann Goering. Goering's mother was the mistress for many years, before and after Hermann's birth , of Ritter Hermann von Epenstein, a doctor who was half Jewish. He grew up in a castle von Epenstein owned, and where his cuckolded father lived aliong with his mother, her lover and Hermann and his siblings.