The Moulin Rouge! actor stars in new BBC thriller Exile as retired journalist Sam, who is suffering from Alzheimer's disease, but he has now admitted the part was supposed to be played by Postlethwaite, who died in January (11).
Broadbent reveals Postlethwaite was the first choice for the lead role, but he had to quit the TV show as his health failed - and the actor admits the casting revelation convinced him to accept the job.
He says, "I came on later and Pete Postlethwaite was down to play Sam. Suddenly he couldn't do it and I had an email. That was my one reason why I knew that obviously it's going to be good if it's good enough for Pete."