A stray cat came into my screened in porch tonight and attacked my cat

Hi all. I'm in need of some advice and I've decided to post this here because I really don't feel like getting flack from the anti-outdoor cats community 🥴

I have two cats that were both strays living on the streets when I took them in. They were both very unhappy being kept inside after growing up outdoors, so they've become indoor/outdoor cats. Luckily I live at the end of a dead end street with very little traffic or dangerous wildlife, so it's about as safe as it could be.

Recently there's been a stray (I think) cat showing up on my property. Other neighbors have mentioned seeing him for a while, but I only saw him for the first time last week. I heard one of my cats yowling outside and when I went out to get him, the stray was in my yard. A few nights later, I went out to grab my cat when it started getting dark and both he and the stray were sitting in my front yard, not interacting. The stray only seems to come around after dark, so I've been bringing my cat in earlier to try to avoid him.

I have a screened in porch with a small kitty door to allow my cats to come and go. Tonight around dusk I heard a HUGE commotion out on the porch and ran out there to find the stray inside the porch, but he ran out the kitty door when he saw me. My poor boy's fur was everywhere and he had peed and pooped himself. It was really upsetting, but luckily he doesn't seem to be hurt. No bites or scratches as far as I can tell. But it sounded terrible.

I chased the cat off my property but I'm not really sure what to do from here. It really concerns me that he's bold enough to come into my house. The strange thing is, I've had my female cat for 7 years and have never seen this stray come around before. It's only been since I took my male cat in 3 months ago (but he's only been allowed outside for the past few weeks) that he's started coming around.

The only solutions I can think of are to start bringing him inside earlier and to block the kitty door at night once both cats are in. I'm not as worried about my female cat. She's tough as nails and the stray has never seemed to bother with her. But my boy is a soft little lovebug and I really don't want this cat near either of them.

If anyone has advice on how to keep this cat away, I'd be really grateful!

TL;DR: Stray cat came in through the kitty door onto my screened in porch and attacked one of my cats.