DH said that there was another cat outside the side cat flap. I went outside and recognised the back end of Thunderthighs as s/he strolled off.
Thunderthighs visited our garden a few times last year, and caused the fence to creak alarmingly when s/he leapt upon it. I've only ever seen his/her long fluffy grey haired tail and back legs, so I've no idea what sort of cat s/he is.
Thunderthighs is also the cat that Izzy got into a fight with a few weeks ago. We think thought it was him/her because of the mass of grey fur (mixed with the mass of Izzy fur) in the driveway.
The kittens have been very interested in looking out of the cat flap, ever since we showed them how to come in that way. The flaps are programmed to let the kittens in, but not to let them out. Now when we take the kittens out in the garden, with their jackets on, and on leads, we let (by which I mean "only let") them come in the cat flap. This is so that if they do escape and do ever get chased by a cat, they will be able to come in at speed.
Anyway, they had been looking out of the side cat flap when, presumably, Thunderthighs had walked past and stared in. The were most distressed. Their tails were enormous, they were fluffed up, their little hearts were pounding. Izzy had also fluffed up in protection mode, and probably would have gone outside to defend them if DH hadn't stepped in and stopped her.
The 3 cats are all getting on really, really well. Izzy plays with them, she nuzzles them and lets them nuzzle her. All of us are together in the living room in the evenings.
We're so lucky.