Both my cats have made friends with neighbouring cats, always playing in the garden together.
Previously I caught the elder cat letting her friend in the cat flap!( she came though the flap slowly, letting him come in at the same time!)
I'm not bothered time as 2 toms in the close where tormenting her and every single other cat and he was protecting her, plus she hated every other cat she saw. I have spoken with the neighbour and she is fine about it, quiet often he's lying on my bed when I get home!
Now my kitten has made a friend and the same is happening.
Is it normal for cats to do this?