There are only a few places in the area where black kings and easterns come together that they actually intergrade (NC. AL for example and in NC. Georgia). In most other parts or the range, they apparently don't (just like Eastern Milks and Scarlet Kings). Generally the reason is habitat as these snakes don't occur commonly in the higher mountains that separate the east from the black king range.
Blaney (1977) looked at a number of snakes from around Chattanooga and regarded them all as nigra. He didn't see evidence of intergradation until he looked at snakes from closer to Atlanta.
Black Kings often have yellow crossbars even forming a light chain pattern. An Eastern King usually has a broader chain, and they are bigger. Their is also a slight difference in headshape between the two taxa, in my experience. Easterns have a big body and broad head like a FL King, whereas Black Kings are slenderer with a narrower head like a Speckled King.
I would regard your snake as falling within the range of patterns seen in the Black King.
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Chris Harrison