In Chapter 8, during “The Cursed King/Queen” quest (right after weakening the curse), travel back to the Camp at the Capital Gates to see the Foregather appear and, after a brief exchange, abduct Kalikke and Kanerah. Use the portal to travel to Sorrowflow. Have a chat with the Arcanotheign and the Forefather knowing that you can't solve matters peacefully for this achievement, so pick the option to attack him.
Credit to Starsong for their
guide.