The child star's racy new role!

KESHIA KNIGHT PULLIAM, best known as youngest daughter Rudy Huxtable from "The Cosby Show," is all grown up and playing a lady of the night!

According to the Hollywood Reporter, the '80s sitcom star -- now 29 -- will appear in TYLER PERRY's 'Madea Goes to Jail' as a prostitute who befriends the titular character after she finds herself in trouble with the law.

The cast and crew head to Atlanta next month to begin filming. The movie is expected to hit theaters in early 2009.