"The Best of Enemies". A true story of the friendship between a KKK member and his opposite. Coming to a theater soon. Gonna see it?

A deep friendship grew and the KKK member renounced the KKK and they were best friends for decades.

So a KKK member can renounce his views. I believe that has occurred more than once in the real world. Has the opposite ever occurred? Has a person who did not hate become an avid rabid proponent there of and stayed that way until he died?