Actor Glenn Howerton didn't even pretend to be happy when he found out that roommate Rob McElhenney was dating Kaitlin Olson, one of their costars on It's Always Sunny in Philadelphia, early in the show's run.

"I thought he was doing a bit, because he knows that the stupidest thing you could possibly do is to date your co-star," Howerton, who plays Dennis on the series that debuted in 2005, told Variety in a story published Wednesday. "You're compromising the show and everybody's job. If that goes south, you're f---ed, and your whole show is f---ed, and you f---ed everybody. So I laughed, and he was like, 'No, I'm serious. We both tried to stop it, but it was inevitable. We're in love.'"

That really did it.

"All of this is happening while I've got a f---ing cat pooper-scooper in my hand," Howerton, who was cleaning out the cat litter box, recalled. "I was like, 'You idiot! You've got to be f---ing kidding me. You know this is the stupidest possible thing you could be doing, right?'"

Those would have been very real concerns, except that so far it has worked out for the couple. They married in 2008 and share two teenage sons.

McElhenney plays Mac and Olson is Dee in the dark comedy about a demented gang of friends running a bar. They kept their secret from everyone for a while, but their perceptive costar Danny DeVito, (Dee's father figure Frank), said he could feel the shift.

"When we were going on a trip or something like that, you got the feeling that they were kind of gravitating toward each other in a cool way," DeVito said. "Every once in a while, people who are supposed to be together wind up together."

Still, Charlie Day, who's behind the character of Charlie admitted that he had no clue what was happening right in front of him. He and his own wife, actress Mary Elizabeth Ellis, who's played the waitress on the show for decades, were already together when Ellis first appeared.

If anyone, Howerton had the best chance of finding out, because of the time Olson was spending at he and McElhenney's place — under what he later realized were false pretenses.

"How did I not see this was happening?" the actor asked. "She would always come over and then would get too drunk and sleep there. In retrospect, she wasn't really that drunk; She was just using that as an excuse to stay at our apartment. And then Rob would disappear for a couple of nights, and I'd be like, 'What's going on?' He'd tell me he went out with some girl, just making s--- up!"

Their Emmy-nominated show has remained consistent, too. In 2021, it became the longest-running live-action sitcom in TV history.