Actress-producer Dia Mirza has joined the cast of actor Sanjay Dutt's biopic, being helmed by Rajkumar Hirani.Dia shared the news on Twitter, saying she is happy to be on board for the project.She posted: "The happiest place in the world is on a Rajkumar Hirani film set. Sanjay Dutt biopic, Ranbir Kapoor, Vicky Kaushal." Ranbir, who was last seen on the big screen in filmmaker Karan Johar's multi-starrer "Ae Dil Hai Mushkil", will essay the role of Sanjay in the upcoming biopic. Dia also shared an image of the cast cutting a cake together on the set. Earlier, Hirani had shared that the first shot for the biopic has been taken and there is excitement among the film's team. He had tweeted on Saturday: "First shot taken now for Sanjay Dutt's biopic. Canning a very funny scene. Excitement in cast and crew."