The film that is set to hit theatres on November 11, will see Shammi and Ranbir sharing the screen space together for the first and the last time.
The duo will be seen together in a 'jugalbandi' where Ranbir will be playing a guitar while Shammi will play a shehnai.
"I was fortunate to get close to him and work with him. He is irreplaceable. It is a loss to the film industry...it is a sad news," Ali told reporters outside his residence.
The late actor was on dialysis when he shot for the film in Delhi with Ranbir, who essays the role of a small-town boy dreaming of becoming a rock star.
Shammi had earlier said that playing shenai had always been his passion and was happy to show skills in a Gen-Y movie.
A computer enthusiast, as he called himself, he was also one of the firsts from Bollywood to join Twitter, introducing himself to fans as a "renaissance man, retired actor and computer buff."
The 79-year-old actor passed away yesterday due to kidney failure at Mumbai's Breach Candy Hospital and was cremated today at Ban Ganga crematorium.
Besides the whole Kapoor clan, Bollywood celebrities who were present for the last rituals were Amitabh Bachchan, Aamir Khan, Priyanka Chopra, Madhuri Dixit, Anil Kapoor, Vinod Khanna, Danny and Shatrughan Sinha.
Actors Fardeen Khan, Tom Alter, Tinnu Anand and industrialist Anil Ambani and Filmmakers Satish Kaushik, Sudhir Mishra, Sanjay Leela Bhansali, Prakash Jha, Rakeysh Omprakash Mehra, Ashutosh Gowariker, Ramesh Sippy with son Rohan, Subhash Ghai and Nikhil Advani also paid tributes to the late actor