Revenge of the Sith established that all the Clones became Jedi-murderers thanks to one secret code-word implanted in their brains. Or, at the very least, one specific Clone: Captain Rex. The weird thing is, 15 years after the fact, nobody expected that some of those heroes might turn out to be the Clones.
The opening crawl of Revenge of the Sithbizarrely told Star Wars fans there were "heroes on both sides" of the Clone Wars.