Kaitlin Olson and Rob McElhenney. (FRED PROUSER/REUTERS)

Kaitlin Olson and Rob McElhenney are expecting a baby boy, the couple told People. The “It’s Always Sunny in Philadelphia” actors’ first child, son Axel, was born last September.

“We found out I was pregnant during my mom’s birthday weekend in Ojai,” Olson told the magazine. “I was instantly so proud of this baby for already knowing how to make someone else’s special day all about him.”

It’s certainly been a baby-tastic year for the cast of the hilarious, non-child friendly FX comedy. Glenn Howerton and David Hornsby both welcomed sons this year. And Charlie Day and Mary Elizabeth Ellis are expecting their first child this December.

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GALLERY: Click the image to see photos of the 2011 celebrity baby boom.

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