Last week Kaitlin Olson and Rob McElhenney of Always Sunny In Philadelphia expanded their family. The actors who play Mac and Dee on the hit FX show welcomed their son on Thursday, April 5. Born at 1:15 a.m. in their Los Angeles home, the couple named their son Leo Grey McElhenney. Leo joins 19 month old brother Axel Lee.

Kaitlin Olson posted a picture of their new bundle of joy on her Twitter page. Leo Grey McElhenney...born April 5th after 23 very very long hours. We're in love, says the photo caption.

Olson's cute photo follows some pretty hilarious Twitter posts.  Ten days before giving birth to Leo, Olson tweeted, Baby due in 5 days, my son has a bad cold, I'm on crutches and I just got a piece of quinoa in my eyeball. Cut the shit, God.

Olson and McElhenney have been working on It's Always Sunny In Philadelphia since 2005. During season six in 2010, Olson brought her pregnancy with Axel into the series. The gang had an episode entitled Who Got Dee Pregnant? where they try to recall a hazy Halloween party to determine if one of them might be the father.

Season eight of It's Always Sunny In Philadelphia is set to air in the fall of 2012. No word if Olson as character Dee will appear pregnant in the upcoming season.