Kaitlin Olson & Rob McElhenney: "We're Having A Boy!"

It's another baby boy for Kaitlin Olson and hubby Rob McElhenney!

After welcoming their first child, Axel Lee, 13 months ago, the couple tells People that they're expecting another son in the spring, and Olson couldn't be happier to "add another set of balls" to her "very, very male world."

"We're so happy that Axel gets to have a brother so close in age," Olson tells the magazine, revealing that baby number two is already making his mama proud.

"We found out I was pregnant during my mom's birthday weekend in Ojai," Kaitlin shares. "I was instantly so proud of this baby for already knowing how to make someone else's special day all about him."

Married since 2008, Olson and McElhenney both star in FX's It's Always Sunny in Philadelphia, and apparently, there's something in the water over there!

Co-stars Glenn Howerton and David Hornsby each welcomed sons in September, with Charlie Day and Mary Elizabeth Ellis expecting their first child in December.