Pretty straightforward POD here. Freddy 3 doesn't acquire cancer, and his OTL reign of 3 months goes on for a longer period of time. In OTL, he died at the age of 56, so presumably he had quite a few years left in him (and if his father's health is any indication, a good two and a half decades!).
Frederick III and his wife Victoria were relatively liberal minds compared to the Prussian and German establishments, and the Emperor himself was Anti-Bismarck and sought to lesson the Chancellor's power.