Pilot reported ground agent finished loading the aircraft and stepped off onto the ramp; when the aircraft tipped on its tail and sustained damage. The manifest under reported 1079 lbs. of payload causing an aft CG exceedance and overweight condition.

Narrative

Flight plan was to depart ZZZ1 empty. Fly to ZZZ2 pick up 3 passengers and supplies. Follow to ZZZ to pick up additional supplies. Then fly to ZZZ3 to drop off and return empty to ZZZ1. Upon arrival I had shut down the aircraft and had passengers deplane. Our agent in ZZZ and passengers helped unload all the cargo we had brought and placed on the ground. We went to load the cargo back with the additional cargo from ZZZ onto the aircraft. Once the aircraft was loaded I was getting ready to close the aft cargo door. Our agent was still on the aircraft loading the last bag from the front door into the cabin. The agent stepped off the aircraft and the aircraft sat onto its tail causing rudder damage and strake damage. I contacted my director of operations to notify him of the incident at XA:45. Our agent began unloading the aircraft and took it upon himself to weigh all items that were brought from Person 1. After the incident happened; it was discovered an additional 1079 lbs were added to the aircraft that was not disclosed in the manifest. At this point the aircraft was out of CG and with the additional 1079lbs of undisclosed cargo weight it is my belief the aircraft was over weight as well. My manifest that was provided to me prior to departure was short 1079lbs.