Mary Steenburgen joins the cast of <i>Last Vegas</i>Mary Steenburgen has signed on to star in the CBS Films comedy Last Vegas for director Jon Turteltaub.

The story centers around Billy (Michael Douglas), a longtime ladies man who is finally settling down and getting married in Las Vegas, to a woman half his age. Robert De Niro, Morgan Freeman, and Kevin Kline are playing Billy's old friends who reunite in Sin City for the nuptials.

Mary Steenburgen will play Diana, a Vegas lounge singer who gets too close to Billy before his wedding. Diana also becomes involved in a bizarre love triangle when Robert De Niro's Paddy takes an interest in her as well.

Jon Turteltaub is directing from a screenplay by Dan Fogelman. Laurence Mark and Amy Baer are producing, with Nathan Kahane serving as executive producer. Production is scheduled to begin this fall in Las Vegas.