What was found
PILOT GOT FUEL IN MORNING AND L WENT TO GO CHECK ON MECHANIC THAT WAS WORKING ON A SEPERATE ISSUE. PILOT NOTICED A FUEL TRUCK PULLNG AWAY SO PILOT WALKED OVER TO WINGS AND DID A CHECK OF THE CAPS AND THEY BOTH SEEMED TO BE IN PLACE. WHEN PILOT CAME BACK IN THE EVENING HE DID HIS NORMAL PREFLIGHT WALK ARAOUND AND AGAIN EVERYTHING SEEMED TO BE IN PLACE. PILOT LOADED CARGO AND TAXIED TO THE RUNWAY FOR TAKEOFF. AFTER LIFT OFF HE WAS CONTACTED BY THE FBO WHO SAID THEY SAW SOMETHING COMING OUT OF HIS RIGHT ENGINE/WING. PILOT LOOKED AND SAW THAT THE FUEL CAP WAS MISSING AND TURNED BACK TO THE AIRPORT AND LANDED AGAIN. AIRPORT OPS CHECKED THE RUNWAY AND FOUND THE CAP ON THE APPROACH END OF A SMALLER RUNWAY HE USED TO TAXI.