Prince Harry writes in his memoir about killing 25 Taliban fighters in Afghanistan.
He served as a forward air controller and attack helicopter pilot.
Harry says he's "neither proud nor ashamed" of the kills.
The army taught him to view the Taliban as "chess pieces."
Harry's second Afghanistan tour lasted six missions.
He wanted to return home with a "clear conscience."
The Spanish version of the book was mistakenly released but quickly withdrawn.
Key excerpts were published by media outlets.
The full book is set to be released next week.
Harry's kill count has sparked debate.