"One day over coffee Kunal Kohli said that he had an idea which he really loved but it was not developed. It was just a one line story. He told me it would be an entertaining love story with the same two actors in three different time periods," Shahid said in a statement.
Shahid says initially he didn't understand the time concept in the script.
"I told Kunal that I didn't understand (the time concept) and asked him to explain it to me. He then explained..."
Also starring Priyanka Chopra, the story is based in three time zones between 1910 and 2012. The film will hit the theatres June 22.