Alas, genetic tests finally proved that he was indeed all-Chimp, but apparently from some isolated sub-group in the depths of Africa.
There is also an amazing story about how Stalin allegedly set his scientists up to try to create an "ape-man" hybrid in the 1920s (the stronger to be able to work)...needless to say, they failed to successfully impregnate female apes with human sperm....something only a lunatic like Stalin could believe was possible....
Someone, I don't recall who, posted some information on that recently. Maybe he'll post a link.