Bollywood actor Abhishek Bachchan is said to be playing his megastar father Amitabh's father in the upcoming movie "Pa".

Those working on the production are not permitted to speak about the film as per contractual rules. However, a source from the production house has revealed that "Amitabh plays an alienated and slightly retarded son of Abhishek" in the film.

Helmed by adman-turned-director R. Balakrishnan, popularly known as Balki, the film has its sets shrouded in secrecy and especially Big B's look in the film.

The 66-year-old spends around five hours a day in make-up prosthetics specially created by make-up men flown in from London and the whole project is being kept under wraps at present, with no-one from outside the unit being allowed on set.