It's always a scary time. But as he's been out on supervised visits so many times he'll be fine. Ideally let him out early in the morning (before feed time) and let him explore for a few mins, then bang his food bowl or shake the crunchies and he should re-appear! We have always had a cat-flap though, so not sure about your situation. Keep an eye on the door!

Also a good idea to sprinkle some of his litter around outside. They can smell it from a long way a way.

Ian.

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"Always turn and look when your cat gazes behind you with that intent look in her eyes. Some day there might actually be something there." - T.S. Eliot