Amy Poehler and Will Arnett Expecting a Baby

Baby Mama star Amy Poehler is about to be one herself. The Saturday Night Live regular, 36, and her husband, Will Arnett, are to become first-time parents, their rep Lewis Kay confirms to PEOPLE. The baby is due in late fall. The couple have been married since 2003. This has been a big week for Poehler. Baby Mama, costarring Tina Fey, landed in the No. 1 box-office spot this weekend, and her Nickelodeon show, The Mighty B, also debuted. Arnett, 37, is currently shooting the big-screen comedy When in Rome with Kristen Bell.