The late superstar has a prominent role in the movie. It is almost ready, but Tyagi wants to release the film on Rajesh Khanna's birth anniversary.
"We can release the film at any time, but we want to release it on Dec 29. Since it is a Saturday, we will be releasing it on Dec 28, just a day before Kakaji's (Rajesh Khanna) birth anniversary," Tyagi told IANS.
The director says Rajesh Khanna has left a letter behind, and that shall be opened just before the release of the film.
"Kakaji has left a sealed letter behind him, which he wanted us to read before the release of the film. So we will be opening his last letter either on his birth anniversary, or just before the release," he said.
"We have no clue what he has written in the letter. I am only thankful to god that we got an opportunity to work with him," he added.
For his role in "Riyasat", Rajesh Khanna is said to have sat and watched the DVD of the 2005 Amitabh Bachchan-starrer "Sarkar".
"Before starting the film, he watched Amitabh Bachchan's 'Sarkar' as he is also playing godfather in the film. It's a very different subject and he had shot almost 95 per cent of the film.
"The entire nation will hear Kakaji's voice in the film," said Tyagi, who had started shooting the film in February 2011 and finished it in October.
Rajesh Khanna died in July after prolonged illness and a liver infection. But he had wrapped up most of the shooting for "Riyasat".
"Kakaji shot most portions, the ones I wanted. But yes, we were tempted to shoot more. And if his health permitted, we would surely have shot all of it. Then all of a sudden his health started deteriorating and he left all of us suddenly," he added.
"Riyasat" also features Gauri Kulkarni, Aryan Vaid, Aryeman Ramsay and Raza Murad.