Last night his brother Noki slipped out the door while I was trying to get the dog inside. This isn’t a huge deal, he used to be a partial outdoor cat, I usually just wait and he comes back in an hour or two. Here’s the trouble though, when he came back, this one (Scooter) decided he’s never seen this cat in his life and will therefore attack and chase him viciously. I managed to wrangle Scooter into his carrying cage and get him in my bedroom. He spent the night with me with the doors closed, and when I woke up they seemed to be sniffing each other under the door and not hissing or howling, but when I opened the door all hell broke loose. Scooter will still not leave him alone if he sees him. I tried rubbing Noki with the towel from Scooters cage trying to get him to smell more familiar, but I don’t know what else to do. They’ve always gotten along really well and their play fights never involved hissing and howling. Scooter lost a whole claw in the exchange last night. Noki seems fine but is hiding in a closet and I had to bring him food because Scooter won’t let him come downstairs.

Update: Thanks to everyone for the suggestions! I kept Noki in a separate room overnight with a litter box and food/water. I fed Scooter and him treats on either side of the door. This morning I switched and put Scooter in the room and let Noki out. When I got home I fed them both treats under the door and then cracked it so they could see each other. No hissing or aggression so I let Scooter out and they finished the treats with their faces touching. After the treats were finished, Scooter gave a quick hiss and Noki walked off but there was no chase and no fighting. I think I’m on the right track! Noki is still hiding so I’m going to keep them separated and continue feeding them treats together until I feel like they are back to normal. This community is awesome, big thanks to everyone who commented♥️