Sorry, I forgot to say that I think I know what a king cup is - it's where a queenless coloncy tries to make a queen out of a drone cell in desparation.
I found some partially made queen cups on a frame in a (presumably) queenless colony with one beaut of a sealed ? queen cup. I don't want to destroy it just in case. This is a follow on from a previous post about laying workers/drone laying queens.
I am interested in what a king cell looks like.
Kingcup is a common name for Marsh marigold,
Caltha palustris!
I have never heard the term in connection with beekeeping, nor the term "king cell".
A Queen cell made from a drone cell looks a lot like any other emergency cell, I should imagine: rather small, rather perpendicular to the surface of the frame compared with supercedure or swarm cells, on the surface rather than hanging down underneath the frame etc. If it really was from a drone cell then I guess the only difference would be that the base of the cell, and the surrounding cells, would obviously be larger drone cells.
A Google image search on "emergency queen cells" should help, esp. if you keep the words in quotes. In general I'd say that such cells have a rather messy, hasty look, and there are usually quite a lot of them at a similar stage, and quite small.
Are you sure that your queen cells are in a queenless colony? Lots of colonies are making swarm cells at the moment despite peoples' earlier attempts to artificially swarm them. And if there really is only the one, nice-looking cell that's actually finished, then it might be a supercedure cell. In both cases there will be a queen present (apologies if you already know all this!). I have never seen an emergency queen cell made out of a drone cell, but they would presumably do this only if they had been queenless for a long time and/or had laying workers.
I would firstly check whether there's any chance they could be swarm cells, and take swarm management action accordingly. If it seems more like emergency or supercedure cells, leave the good one and wait and see.