Cessna 182 pilot reported an engine malfunction during cruise; the pilot returned to the departure airport and landed. The pilot discovered the propeller control cable had separated from the propeller governor.

Narrative

We were on a day VFR sightseeing trip out of ZZZ bound to ZZZ1. We were cruising at 3;500 MSL about 15 minutes into the flight when the engine 'revved' momentarily and then steadied at about 19' of MP (Manifold Pressure) and 2000 RPM. I immediately turned southwest with the idea of landing either at ZZZ2 or ZZZ.I went through the emergency memory items: checked magnetos; ensuring we still had fuel in our tanks; carburetor heat; switching fuel tanks; and very tentative changes with the throttle; propeller control and mixture control. The throttle did respond but we were not able to increase our power output.We were able to maintain our altitude and I headed back to ZZZ. I requested priority handling with ZZZ Tower; who gave me a clearance for a straight-in approach to Runway XX even though the active runway was XY. I told the Tower that we were going to maintain our altitude even though it took us into the Charlie airspace for ZZZ3. We set up for and did a normal landing on XX without any difficulty and taxiied back to the hangar. The next day; we discovered that the propeller control cable had separated from the PCU5000 prop governor. The normal pre-flight inspection was normal; as was cycling the prop during the runup prior to takeoff.