Air taxi Citation pilot reported after landing and parking they observed a fuel leak and the aircraft right main landing gear door was missing.

Narrative

I was PIC on Aircraft X. We were assigned a reposition flight from ZZZZ to ZZZ. We departed ZZZZ ; we landed in ZZZ. The taxi; takeoff; en route and landing were all normal.As we taxied in the line crew were pointing at our airplane. I shut down as I normally do. The customs agent met us at the door. He checked our passports. While he was doing that the line crew said we were leaking fuel. The customs agent said we were good to go.We exited the airplane and I saw fuel leaking from near the right main landing gear. The fuel was a stream about the size of a pencil in diameter. I asked the line crew if they had anything to catch the fuel in. They proceeded to get a large container to catch the fuel. The line crew; airport maintenance personal and the airport fire department contained and cleaned up the fuel.I had the line crew connect a power cart to the airplane and began transferring fuel from the right tank to the left. I assigned my copilot to monitor the transfer.I contacted our operations as well as our maintenance department and advised them the airplane was leaking fuel.While talking to our maintenance department; I saw that the right main landing gear door was missing. I noted there was no other damage to the airplane. No scratches; dents or anything appeared to be damaged just the missing gear door. I had a conference call with our chief pilot and director of maintenance. They asked me to explain what happened. I told them what I knew. We took off; flew and landed with no anomalies. They asked if I hit anything. I advised that I hadn't. I was not aware of anything hitting us either. I asked if I should contact the FAA. They advised there was nothing to report. I had and still have no explanation of how the gear door came off.