Introducing a new cat, will mine ever be the same again?

Never seen a cat get that mad about another cat for long.Cats are territorial.People do not think about it because they are not like an 80lb pitbull or doberman haha.Give it a couple of days.Many many years ago I had a baby kitten (male) that could barely crawl and I was feedin with an eyedropper.We ent to visit my Grandmother 500 miles away and I had to bring the kitten.My grandmother and parents were was worried that her HUGE tomcat that fought other cats constantly would kill it or run away from home.I put the kitten in front of him.The kitten hissed and bowed up.The HUGE Tomcat just looked and sniffed at him.Within the hour the Tomacat was cleaning the kitten as if he was the mother.It shocked everybody.That night they cuddled up and slept together.A week later when we went home the Tomcat kept meowing when we left with the kitten.He actually missed his new buddy for a few days.I also have seen a new cat be introduced and the regular cat leave and never comeback after a couple of days so watch out for the mad cat.