General aviation pilot reported seeing a fixed wing RC plane operating within Class C airspace at approximately 1;500 feet.

Narrative

I was piloting Aircraft X at between 1;400 and 1;500 ft. flying north over ZZZ. I am an Air Traffic Controller and was giving a fellow controller and non-pilot a scenic flight. The passenger requested we fly over ZZZ to take some pictures. As we approached the airport we were instructed to pass midfield northbound for IFR departures. As we crossed north; fighter jet was lined up for a Runway XX departure. My passenger was going to take a video of the fighter jet departure off our right wing as we turned east bound to parallel the runway. Prior to our turn we both noticed a red and white RC plane climbing to an altitude just below us about a half mile off the nose. The passenger turned the camera around and captured the RC plane descending and then maneuvering below us. We then did a 360 and the RC continued to make a low approach and then climb back to an altitude below us and was not a factor. I would not describe this as a NMAC but it was alarming to see the RC plane that high inside Class C airspace. The event took place over a local RC club operating facility.