I've recently moved into DPs house with my 2 dcats, DP also has a cat. We followed advice on introducing cats gradually - mine were kept in one room for the first 3 weeks, we had feliway diffusers and did scent swapping, before short supervised in person meetings (with Dreamies to make positive associations). However, DPs cat has remained hostile to mine and has attacked both of them on separate occasions. He is lovely with humans but has always been a fighter with other cats, I had really hoped he would learn to tolerate mine. Is there anything we can do? They have separate food stations, litter trays etc. One of my cats doesn't go out as the cat flap is often guarded, my other cat rarely comes in the house for the same reason.