During a skydiving operation, the aircraft was slowed to slow cruise flight for a parachute jump. As skydivers were moving to the exit door for a group jump, the d-ring of one skydiver’s reserve parachute became entangled on a protruding cabin door support bracket. The reserve chute deployed & was caught in the slip stream. The skydiver was then pulled from the open door. He impacted the right horizontal stabilizer, fell 4000 ft to the ground & was fatally injured. Most of the right stabilizer was torn from the aircraft. After its separation, the aircraft entered a dive & the remaining skydivers jumped from the plane.