don't take kitty back to the shelter! trust me, they WILL get along.
keep them in separate rooms for a few days. let new kitty explore his new space and get comfortable with it before throwing Rex into the mix. the best thing for cats is to give them their own space until they're ready to share spaces with one another.
get a blanket or something that Rex really likes to lay on and put it in the room with new kitty. this will help introduce his smell. do the same thing for Rex - rub a towel or blanket over new kitty and let Rex smell it.
after a few days, switch them - give Rex new kitty's space and vice versa. try to be patient - new kitties never like each other right away.
after 2 days or so, they should be ready to meet. make sure they are doing normal kitty things and that they're comfortable in their own spaces before letting them interact. there will be growling and hissing, and they might actually go after one another, but don't let them fight. give them treats and encourage them in a positive manner to be nice to one another.
here's a link I found with some helpful information.
http://www.cathealth.com/multi-cat-households/how-to-introduce-a-new-cat
Re: :: reba :: RE: new kitten
Cheddar absolutely hated Muenster at first. I felt so bad - Cheddar would give me the most evil stare when Muenster was around, then just leave the room. I felt like I was cheating on him.
Anyway, it didn't take long until they were tolerating each other, then playing together, then snuggling. They are the best of friends now. I can't post pics from work or I'd post some of their best snuggly poses.
Hang in there, Reba!
I followed Mandee's advice when we brought Chloe home, and it worked, to some extent. Our cats have never been best buddies (like Cheddar and Muenster) but they tolerate each other, and Chloe still tries to clean Meka's head sometimes.
But, keeping Chloe off in her own little room for a few days and doing the switching thing helped a lot. When we first brought Chloe in Meka was having NONE of it. But over a few days she calmed down.
We'll just not tell H about this little fact, m'kay?
The Daily Nugget
Cycle 12, IUI #1 - 33m post wash 10/15/10 = BFN
Cycle 13, IUI #2 - 15m post wash 11/16/10 = BFP, missed m/c, D&C 1/3/11
Cycle 15 - 18, IUI #3-6 = BFN
Cycle 20, IUI #7 = BFP!, missed m/c 9/14, D&C
DE-IVF Aug. 2012: ER 8/30 11R, 7M, 4F; ET 9/4 returned 2
Beta 9/18 #1-820, #2-1699, #3-7124
10/1 1st u/s measuring right on track, 125 bpm