Not true. Just a myth.
You may want to do a little research, and not believe everything you read on internet.
1st. Hitler had great grandparents too...his geneology reveals many jewish names (not all names mean they are jewish, but the many he has (some of these last names were in Jewish training camps and executed).
Such as: Huemueller, Artner, Kaufmann, Tecker, Hagen, Anderl, Sillip, Walli, Decker, Hiedler just to name a few...all listed as jewish and all surnames of Hitlers great grandparents:
http://genealogy.wikia.com/wiki/Adolf_Hitler_(1889-1945)
Now go to the JewishWebIndex.com to see how surnames were formed, and then go to the list of JewishGeneology and you’ll find most of them were Prussian jews, and some of these jewish names survived Holocaust like Artner and Huemueller. Not a coincidence and not a myth...Hitler had some Jewish great grandparents...period.