See Will Arnett's Amazing Abs in Up All Night Promo

USMagazine, Thursday, September 20, 2012, 11:45am (PDT)

Even though his nine-year marriage to Amy Poehler is ending, Will Arnett has never looked better!

The actor, 42, showed off his sculpted arms and six-packs abs while shooting an Up All Night promo with his costar and on-screen wife, Christina Applegate, 40, in West Hollywood August 11. "Will looks really good right now. Everybody is talking about cut he is," a source tells Us Weekly. "He's been working out and his skin is really great."

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Despite separating in early September, a source close to Arnett and Poehler told Us "they have a lot of respect for each other," and another insider called their split "very amicable." Indeed, Arnett and his sons, Archie, 3, and Abel, 2, were spotted attended Poehler's 41st birthday party over the weekend.

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Even still, the couple's separation shocked both friends and fans alike. "The past few months have been rough for them," an insider told Us, "but I don't think anyone in their circle saw this coming."

Poehler is currently promoting the sixth season premiere of Parks and Recreation, though she hasn't yet been asked to address her recent separation. The Saturday Night Live alum is, however, happy to talk about her two boys with Arnett.

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"I'm pretty strict with them," she said on the Ellen DeGeneres Show September 20. "I'm big on manners and 'please' and 'thank you.'"

Even still, "They are boys, so they're kind of crazy," Poehler admitted. "Mothers come over with daughters and we have play dates. My house is a little crazy -- everyone's kind of running around, jumping off furniture. They'll bring there daughters over and the daughters will be like, 'Should we sit in the corner and cooperate?' My guys are like, 'I made chocolate soup.' They will just make dirt soup. And the girls are making like a birdhouse out of organic materials.  It's different."

Arnett's Up All Night premieres September 20 at 8:30 p.m. EST on NBC, while Poehler's Parks and Recreation premieres on the same network at 9:30 p.m. EST.

This article originally appeared on Usmagazine.com: See Will Arnett's Amazing Abs in Up All Night Promo