Saw flying rectangular metallic object then it vanished into thin air

Driving out of the mountains last week I saw a metallic flying object that looked like a flying toaster but larger. It had a dark area to the backside or left on the object. When I stopped my truck to record it the thing vanished in a blink of an eye. There were no clouds in the sky or trees in the way to block my view. It happened so fast my son did not see it. The flying object was only 300 feet high at the most. It was moving fast laterally like it was paralleling our trucks travel direction observing us. I took a picture of the sky where I last saw the object after it disappeared. I stood there for a few minutes trying to figure out where the thing went or see if it was going to reappear. No sound I could hear like a plane. Right after it disappeared there was a white jet or drone that flew overhead where the object disappeared from. The drone looking thing was high in altitude compared to the flying toaster shaped metallic object I had seen. The flying toaster object was approximately 20 ft long and 10 feet tall. No flashing lights but there was a dark area on the back or left side of the object. It was traveling fast from my left to right in the sky.