Hirani has worked with Dutt in "Munna Bhai" series and now he will be chronicling the 56-year-old actor's life on the big screen.
"I have worked with him (Dutt) in three films. I am not saying I am friends with him but I know him. But I respect him and he respects me and so possibly he chose me to narrate this story," Hirani told PTI.
"Last time when he was here I narrated him the whole script... He is aware about what's happening," the filmmaker said.
Dutt's celluloid and real life have seen a lots of turbulence but his involvement in the 1993 blasts case ended with a prison sentence, affecting his family and fans both. However, he is expected to walk out of jail soon.
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"In any biopic of two-and-half to three hours of the film you cannot show the entire life of a person. We are selective in showing what the world wants to hear about him. Like in 'Gandhi My Father', they chose to show his personal life and not the struggle," Hirani said.
"It is at a very early stage... One draft of the script is done. And we have signed Ranbir Kapoor. But beyond that nothing has been done," he added.
In real life, Dutt has got married thrice, so there might be more than one heroine in the biopic.
To which, Hirani said, "We are still working on the script... There will be changes in the script. We are yet to take a call on that (heroines)."
Dutt might co-produce the film but the logistics are yet to be finalised. The film will go on floors this year and would release around Christmas 2017.