Cat besotted by my cat.

This is weird. I have two 7yr old neutered boys and their 9 year old spayed mother. They're all free range cats. For the last 3 months or so, one of the boys has been getting into scuffles with another cat. He'd stroll back in completely unruffled so I suspected not serious and although I regularly heard the cat 'crying' outside I never saw it till a week ago.
I'd gone out after hearing a scuffle and my cat walked back through the fence followed by a tiny (but adult) neutered tom. Everywhere my cat walks, the little one walks behind him. If he got too close, my cat cuffed him and he rolled into instant submission.
When my cat went into the house I attempted to shoo the cat away. He sidestepped me. I put my foot out to stop him and he jumped over my leg and followed my cat into the house where he sat gazing at him and trilling gently. He was completely relaxed when I lifted him up and put him out but he came straight back in so I ended up locking the catflap although I could hear him crying outside.
The next morning my husband woke me with 'come and see this!' I'd seen it.
My front door is always open in good weather. The newcomer spent the day following, trilling and gazing (although I kept him away from the food bowls)
That night I locked him out but 'cracked' and unlocked the flap at around 2am as he was crying so pathetically. It's not that I wouldn't welcome him as an addition to the household, it's just that he's such a sweetie, someone somewhere must be missing him.
He's been here for a week now. The other cats like him. He goes out but never for more than about 30 minutes and he's still absolutely besotted. I can hear him trilling now.
Has anyone encountered this behaviour before because I haven't. If it's relevant there is a possibility that he's my cat's father.

Next question. What to do? Finding the owner may be possible if I go door to door but getting him to return home may not be.
As far as he's concerned he is home.

RESPONSE:

This behavior is not unusual. The new guy has made a friend and wants to be with him! They may be related but it is impossible to know for sure. When something like this happens with us, we keep the new cat and put up notices. Rarely does someone respond but if they do, we let them know what is happening. The only way to stop this is for the original owner to keep their cat indoors. If they don't want to (or don't seem to care)we just keep the new guy. Since this kitty seems happy living with you and since you don't mind, give him the love and attention he has been missing and let him stay with his new friend! If the original owner is truly a cat lover, they will be grateful you have taken such good care of their cat. If they aren't, they don't deserve him!

Donna
House Full Cats Mom