Eclipse, Full Moon or What????

I have a two year old Mane Coone and a little over a year old Russian Blue. Last night for the first time a black cat came to the glass sliding door and my two cats began fighting and even this morning are still growling at each other. The Russian Blue is much more laid back, but this morning keeps growling at "Amelie". I can't figure it out for the life of me, they have been around each other for over a year. Now granted, the first week last year was a challenge, but we got over that real quick.

I have kept them separated all night and now this morning, the two just keep growling and seem like they'll fight if I put "Krishnamurti" (Russian Blue) down. It is so weird and low and behold it was a full moon, a stray black cat...but, how do I resolve this? It seems like they've forgotten that they're buddies, friends and usually play every morning before taking a morning ciesta?? Please help...I'm so confused?????

Sounds to me like what is called "redirected aggression." I don't know too much about it, but I think if you do a search on the forums, you should find some posts that tell you how to best handle it.