Christina Applegate can add a new role to her resume: mommy. The actress gave birth to a baby girl last week, her rep told PEOPLE.

"Christina Applegate and fiance, musician Martyn LeNoble, welcomed daughter Sadie Grace LeNoble on Thursday, Jan. 27, 2011, in Los Angeles," her rep said in a statement. "Mother and daughter are doing great."

According to a source close to the couple, they are over-the-moon with the new addition to their family.

"She's a beautiful little girl, and they are so happy and in love with her," the source said.