"Lincoln Bell Shepard is here," Ball's fiance, Dax Shepard, tweeted Thursday. "She has mom's beauty and dad's obsession with breasts. Hooray!!!"
"My new roommate poops her pants and doesn't pay rent...basically Dax pre-sobriety," Bell wrote. "Welcome baby Lincoln."
Shepard, 38, is a cast member of TV's "Parenthood."
Bell, 32, is one of the stars of "House of Lies."