Drone-like sphere follows airplane in clear afternoon sky, then veers slowly away, before vanishing.At my apartment complex, I had just walked out to toss trash in a dumpster, when I heard, and then saw, a Cessna model 172 flying in an Easterly direction, above the trees and housing area nearby. The sky was blue, and without any clouds. The Cessna flew at an altitude that suggested it would land at nearby Fullerton airport. It was perhaps about one quarter mile south of my location.Just a moment after looking at the Cessna airplane, I noticed a mostly round shaped object, about one third the length of the Cessna in size, was flying just slightly higher and behind the Cessna plane. The object was colored mainly white and black, and had a single and very bright white light near its top that flashed regularly, like a beacon or strobe.The object flew on at a slower speed than the Cessna, and I followed it for about one minute as it flew farther away and farther South than the track the Cessna had taken. When the object was then just a tiny point in the clear sky, it suddenly just vanished. I watched for another minute or so, but it never came back.The best thing I can compare the object to would be the flying ‘drone balls’ that are in the Tom Cruise Science-Fiction film called “Oblivion”. The object flew and looked much like those round drones in that movie, though I estimate it to have been much larger in size than those in the film were. Maybe the size of a Smart Car or Fiat 500.I believe whatever this object was, that it was a remotely controlled vehicle. Whether it was of an alien origin, or a secret military device, I can only speculate at this point. But I can say that it is the second time I have seen a drone-like UFO flying in the vicinity of my apartment in Anaheim, seeing another one just last year, also in the afternoon daylight hours. Lastly, I had the feeling it knew it was being observed.