In the 7th Book.... they mention him and Grindelwald a LOT, his Brother, Aberforth goes on about it, and Albus himself says that the two were as close as could be at some point.
Banned for the Pole Position.
Xer0 \^/
LOL, you have it all wrong, mate 
In the 7th book, it is mentioned in Rita Skitter's book (dont know how its spelled), that they were very good friends, and shared all of their ambitions and plans about the future, which they planned to take over power, and Rule by force, removing all rights from Muggles, etc etc etc.
Banned for false assumptions you dirty boy 
"Mr Anderson, welcome back....we missed you...."