This is a new experience for me. I have a nuc that re-queened recently and had 3 supers on it. I have some presentations coming up, so yesterday, I caught and marked "the" queen and reduced the nuc to 10 frames. This is the set up I like because it makes it easy to find the queen quickly and load up an observation hive with little drama. I was doing this earlier today for a morning presentation. I went through all of the frames and did not see the queen. When I looked on the outer cover where I had placed the top super, there was a cluster of bees and 2 queens locked in combat. I picked them up, put them in the observation section of the hive, loaded the rest of the frames and brought them in. I don't know how long they had been going at it before I went in the hive, but it took about 20 more minutes for a resolution. It appears that the marked queen is the loser because she is walking around on the bottom portion of the observation area of the hive and has tattered wings. The larger, unmarked queen is now up on the frame of brood walking around.
I am not sure where the extra queen came from. David has a nuc here at the house trying to get a queen made & mated and I also have one. Both of these should have had queens go up on mating flights somewhere around June 5th-7th. If one of these queens mistakenly went into this hive after her flight, I would have thought she would have been set upon by the guard bees upon entering. I am a bit puzzled.