Looks like a gray rat snake from here...google photos of Pantherophis spiloides, or a young Pantherophis obsoleta (black rat snake). All in the same family,
these & yellow rat snakes too...they start out with the shades of grey blotch pattern, then darken to black or change to yellow...only the gray rat snake
keeps his juvenile blotch pattern. Excellent pet snakes...get bigger than corn snakes, easy to feed. I currently have 2.2 "Florida" rat snakes...mix of yellow
& gulf hammock rat snakes (neighbors in the wild, along with grays), & I've had black, gray (White Oak phase), & Everglades rat snakes (bright orange w/
yellow chins) in the past.
And you're right, he's definitely NOT a king or a milk snake. Better pet too, IMO...I love rat snakes.