So you have your Eccentric Mentor and with his backing you're facing off against the nefarious machinations of the local Evil Sorcerer, when suddenly you learn a shocking truth -- in their youth, rather than being bitter enemies, these guys were best friends! Note that this is about friends who turned evil in the Backstory and are either introduced or established in their first appearance as villains. If the friend turns evil over the course of the work, see Face Heel Turn. Examples