please help! cat suddenly turned into bully

I have two 1-yr-old cats, a boy and a girl, both spayed/neutered. Last night I didn't close the window properly, so the girl jumped out of the window and wandered around outside. This morning I retrieved her and gave her a bath because she was a little dirty. Then after the bath the boy started hissing at her and being really aggressive, refusing to let her eat, and every time she came near, he nearly went wild hissing at her. (But he's perfectly fine when I touch him). My cats have been really good friends, and all of a sudden the boy became a bully, and the girl is in a corner, terrified. It's like they've become strangers.
How do I get the boy to stop hissing at her? Please help!

I agree, your cat that went outside will certainly smell a lot different to the other cat and he will probably feel a bit threatened by these new smells

You need to get their scents mingled again, if you have towels, blankets or t-shirts that are regularly used by your cats, as suggested rub each cat to swap the scents about.

Good luck !

Thanks for the suggestions, but it doesn't seem to be working.
I thought it was the smell, but I gave them both a bath at the same time just now, and the boy's attitude hasn't gotten any better toward her.