EXCLUSIVE: 'It's Always Sunny in Philadelphia' Star Kaitlin Olson Takes ET Behind the Scenes of 'The Mick'

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ET got a behind-the-scenes look at Kaitlin Olson's new comedy, The Mick, where the actress explained the difference between her It's Always Sunny in Philadelphia character and this new hilarious role.

"Sweet Dee is an extremely self-conscious person and cares very much about what the gang thinks about her," Olson tells ET's Ashley Crossan of her Always Sunnypersona. "Mickey doesn't care what anybody thinks. She's much more independent."

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On the upcoming sitcom, Olson plays Mackenzie (aka Mickey), a two-bit hustler from Rhode Island looking for a big score that can turn her luck around. Mickey almost gets her wish when she goes to her sister and billionaire brother-in-law for money, but gets more than she bargained for when the couple flees the country to escape federal fraud charges. Their absence leaves Mickey as the legal guardian to the three high-maintenance children they left behind.

While The Mick has an edge to it that fans have come to expect from Olson, it also comes with a lot of heart, which was a relief for the mother of two.

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"I love It's Always Sunny, and I don't really ever want that to end, and I was able to do both of them," Olson says. "It's nice to be able to do a network show that my family can watch."

Her sons, Axel, 6, and Leo, 4, are also able to have more fun when they visit their mom at work now.

"They can actually sit in this time rather than just be in my trailer, which they are on Sunny," Olson admits.

Joining Olson on the show are Scott MacArthur (Mickey's friend-zoned sidekick, Jimmy), Sofia Black-D'Elia (Mickey's 18-year-old niece, Sabrina), Thomas Barbusca (Mickey's 13-year-old nephew, Chip), Jack Stanton (Mickey's 7-year-old nephew, Ben) and Carla Jimenez (the family housekeeper, Alba).

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"The character I play, Jimmy, is basically the old dog that Mickey brings with her to this brave new world," MacArthur says.

"[Jimmy] considers himself my long-term boyfriend but I do not," Olson adds.

The special premiere of The Mick airs on New Year's Day at 8 p.m. ET/PT on Fox. It's Always Sunny in Philadelphia returns to FXX for its 12th season on Jan. 4.