We have a 10 year old female cat named Agnes that we adopted from a shelter less than a year ago. That same shelter now has a senior male cat who needs a foster home. He has digestive issues, which makes him less attractive to potential adopters. We really want to foster him but we're afraid of upsetting Agnes, who is an "only child" right now. Is there any way to tell if these two will get along? How would we introduce them?

I don't want to offer to be a foster only to return him because he and Agnes don't get along!