While Gregory was showing Rick around the community, he was stabbed by Ethan who was sent by Negan, the leader of a group called The Saviors. Having survived the confrontation he had a discussion with Rick about Negan. Rick eventually told him that they will help them take him and his group down.
During the war between Negan, Gregory is overthrown as leader by Maggie Greene.
Much later on, Gregory attempts to regain control over the Hilltop by trying to poison Maggie. Unfortunately for him, it does not go as he planned and his plan ends up costing him his life. He is hung to death.