I'm dealing with the same problem right now with one of my Graybands. The tip of his tail has become rigid and rather ugly looking. Above that, and below the anus, scales started coming off to reveal raw skin underneath. It probably began from shedding problems, when the last part of old skin on the tail accumulated after not coming off properly.
Upon taking him to our herp vet, he was diagnosed with a fungal infection. He had given me a tube some time ago containing a sort of antibiotic/lubricant that would help with typical shedding problems (including eyecaps) whenever they arose in one of my snakes. He recommended keeping it handy for any such problems. I first began to apply the lubricant, but when scales started coming off on his tail I took him in for an exam. The vet strongly recommended not only getting him off of the lubricant immediately, but wash all traces of it off of the affected area! He gave me a different type of ointment that I now have to apply to the infected tail twice a day for a month. It's designed specifically to combat fungal infection.
He's improving, but the tip of his tail is still hard and we may not be able to save it. But at least the scales are filling back in. He's just gone blue, so we'll see what happens in another week or so.
So, if your king's problem is fungal in nature, the usual treatments for bacterial infections and shedding problems may not work - and might even make matters worse. I strongly recommend getting a professional diagnosis from a herp vet before proceeding with any medicinal treatment. Continued soaking may be okay, though. Good luck!
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MichaelB