swarm returns to hive

Unfortunately down to miserable weather i have not been as regular at
checking my hives. This Saturday just gone I checked the forecast we had 15 degrees plus in the afternoon so i set about my saturday chores part of which meant nipping out for a couple of hours ,, on my return my neighbour met me and told me that one of my hives had swarmed,, the sky was full of bees and that load unmistakable buzz for sure they were swarming but after about half an hour they all returned to the hive clung on all over it and went inside.
I immediately donned my protectives and opened up the hive it was full of bees. I looked as hard as i could but could not find the old queen anywhere but found a sealed queen cell and three open cups,, i decided to leave them and inspect again with my girlfriend the following day hoping 4 eyes better than two in trying to locate the queen, we looked and looked but no sign of the marked queen but what we did find was that the sealed queen cup was now open i shut the hive and have now come to lay myself down at the feet of the forum and beg forgiveness if I've cocked up, and implore help to get me back on track.
baffled!

Is your queen clipped?
Are there any eggs?
The bees have been waiting for a weather window to swarm.
If that QC has had a queen emerge she won't fly for a few days but you will lose a cast if there are more queen cells there.
You have three other hives so they can help out if things go wrong.
I would go back in and take those open cells down and take a chance that you have a virgin queen there.

Basically what has happened is that the bees have swarmed on the old queen but have lost her on the move to a tempory clustering point and have therefore returned to the hive. If you had looked on the ground between the hive and the clustering point it is highly likely you would have found a small cluster of bees with the queen amongst them. Look on the positive side you have the majority of your colony in the hive rather than having lost 1/2 and that these flying bees are going to bringing in loads of nectar.

Possible, but they would have been waiting a week, after the first queen cell had been sealed, before swarming? And with open queen cells there as well means the queen was still laying even after the first cell was capped, which is unusual? But bees do what bees do and there are always the odd exception to the rules. Guessing here that 'open cups' means queen cells with larvae?

Otherwise it could have been supercedure that changed to swarming, but the queen was damaged and was lost.

There will be a simple explanation, I am sure.

Hey guys , no the queen was not clipped and yes there was eggs, larvae unsealed and 3 or four frames of sealed brood including drone brood . I have removed all other queen cells to .Ive also added a new brood chamber with pulled and unpulled wax hopefully this may keep em occupied really don't want to lose em its a really strong unaggressive hive. all advice great fully received.

Same happened to me , 5 days later I inspected the hive again and noticed a mass under the mesh floor, In this mass was the Queen.
I just put her in a nuc as an AS.
That was so lucky. Its certainly worth looking around for her ..