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OTRC: Kaitlin Olson and Rob McElhenney of 'It's Always Sunny in Philadelphia' expecting second child

Kaitlin Olson and Rob McElhenney at the premiere screening of 'IT'S ALWAYS SUNNY IN PHILADELPHIA' on Sep. 14 2010 in Hollywood, CA (FX)

"It's Always Sunny in Philadelphia" co-stars Kaitlin Olson and Rob McElhenney will be adding another son to their family in the spring.

The actress talked about her pregnancy on Twitter Thursday saying, "You guys...look...I'm having another baby. I wanted you to know first. It's a boy and I'm naming him after you."

Olson and McElhenney have a 13-month-old son named Axel Lee. The couple married in September 2008 in Malibu, California. Olson and McElhenney have co-starred together on the FX comedy series "It's Always Sunny in Philadelphia" since 2005.

McElhenney created the "It's Always Sunny in Philadelphia" and developed the idea with his co-star Glenn Howerton. On the show, McElhenney plays Mac, who co-owns Paddy's Pub with friends Dennis Reynolds (Howerton) and Charlie Kelly (Charlie Day). The show also stars Olson as Dennis' twin sister Deandra "Sweet Dee" Reynolds and Danny DeVito as their father Frank. McElhenney gained 50 pounds for the show's seventh season.

The couple's co-star Gleen Howerton welcomed a son in September while Charlie Day and his wife Mary Elizabeth Ellis, who also stars on the series, are expecting in December.

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