Rob McElhenney and Kaitlin Olson (Creative Commons)

Rob McElhenney and Kaitlin Olson (Mac and Sweet Dee) of "It's Always Sunny in Philadelphia" are expecting their second child this spring, People reports. The couple said they will be giving their 13-month-old son, Axel, a baby brother.

“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 joked.

McElhenney, 34,  and Olson, 36, have been married since September 2008. The pair adds to the "Sunny" baby boom--costars Glenn Howerton (Dennis) and David Hornsby (Cricket) each welcomed sons last month, while Charlie Day and Mary Elizabeth Ellis (who play the on-screen awkward pair Charlie and Waitress) are expecting their first child in December.

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

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