'It's Always Sunny in Philadelaphia' Stars Expecting Second Child

Kaitlin Olson and Rob McElhenney

Kaitlin Olson and Rob McElhenney are expecting their new addition in the spring.

It's Always Sunny in Philadelphia co-stars and real-life couple Kaitlin Olson and Rob McElhenney are going to be parents for the second time.

Olson, 36, and McElhenney, 34, who married in September 2008, are expecting their second child in the spring, according to People. The couple already has a son, Axel Lee, who is 13 months old.

“We’re having a boy! We’re so happy that Axel gets to have a brother so close in age. And that I get to add another set of balls to my very, very male world,” Olson said, who added that they found out they were pregnant during her mother's "birthday weekend in Ojai."

The two star in the FX comedy, which is currently in its seventh season, with Glenn Howerton, Danny DeVito and Charlie Day.

Prior to It's Always Sunny, Olson has appeared in Leap Year, Curb Your Enthusiasm and The Riches. McElhenney, who made it onto The Hollywood Reporter's list of top 50 showrunners this year, previously appeared in Lost and co-runs the comedy with Howerton and Day.