Aggressive behavior

I have 3 cats, all males, 2 are neutered & the little one is at the vet today getting neutered. Earlier this week the little one (Toby) had been outside all night long, when he came back in the next morning my other 2 males started fighting, they are 9 & 4 years old & have been living in the same house with no behaviorial issues until this week. Could this aggressive behavior be caused by Toby being outside all night & then coming in with different smells on him? What do i do? I have kept the other 2 seperated for a few hours each day & then after a while they settle down & its back to a peaceful household again until the next morning & the fighting starts all over again. Will this stop after the little one is neutered or is it going to be an ongoing problem? HELP!!

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