The lyrics of the song have been penned by Prasoon Joshi. Although only 19, Siddharth has composed music and worked on the background score of a Marathi film that released last year, and also assisted in arranging music of Deepa Mehta's Midnight's Children.
Bhaag Milkha Bhaag will be the first time the young talent will lend his vocals for a song which will be launched online on Monday.
Although the initial track was recorded last year when the film's shoot began, the final recording took place a couple of weeks ago in the presence of actor Farhan Akhtar, informed a source close to the developments.
When contacted, an elated Shankar who was leaving for Europe confirmed the news, "Initially it was a temporary track which we didn't think we could use. We wanted a voice with a strong emotional pull. After living with the song for almost a year, both, Prasoon and Rakeysh (Omprakash Mehra, director) felt it was perfect to go ahead with. I'm happy with the end result."