Citation III; VI; VII (C650)
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 50; Flight Crew Total 31700; Flight Crew Type 70
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Took Evasive Action
Aircraft
We were cruising at FL380 enroute direct to ZZZ1 our position was approx 80 miles SE of ZZZ. We were given a descent to FL350 as we were starting our descent we got a cabin red master caution light followed by a cabin horn; the light comes on at 8;500 feet and the horn at 10;000 feet cabin altitude. I saw we were depressurizing we both donned our oxygen masks; [requested priority handling] and started an emergency descent to 12;000 feet. I told the copilot to fly and I will check on our passenger and start the emergency QRH procedures. I was able to stop the cabin at 13;000 feet cabin altitude and advised Center that we would like to land at ZZZ. We advised Center that we had control of the cabin and ended our emergency but would still like to land ASAP. We were handed off to Approach Control and landed without incident. We were very busy in the cockpit and were communicating through our oxygen masks on intercom; and PA to our passenger and to ATC.Upon landing we had Maintenance look at the aircraft and checks preformed and could not find a problem with the pressurization system and the aircraft was returned to service and we departed back to ZZZ2 with no further problems.
Citation 650 Captain reported a pressurization issue led to a rapid descent and diversion.