Why would six cats all living in the same house suddenly turn on the seventh cat living there?

[notalone]

I was just talking to a friend of mine who has had her seven cats for a couple of years. They have all lived harmoniously during that time but last week something changed. They have all turned on one of the cats who is now afraid to come into the house and now sleeps outside. This cat was not the last cat to live there so it possibly isn't a hierachy thing. So what can it be? This cat has seriously annoyed the others - but how and why??

Can anyone shed any information on this please

take the one they have fallen out with to the vet for a check up. The other cats may pick on him/her if it is sickening with something as they smell different.
HTH

I would second getting the cat who is being attacked checked out at the vets asap.

Cats pick up on illness, as the ill cat doesn't smell right to them.

yes it sounds like they have spotted a weakness. this could be an illness. get her to the vet asap.

Oh, we never even considered it could be an illness. I will call her now and urge her to get the cat checked over. Thank you!