Karan was apparently keen to have Tarun as his associate director on the project.
The film has four different directors - Zoya Akhtar, Dibakar Banerjee, Anurag Kashyap and Karan Johar.
A source says, `It will be a landmark feature film this year as it releases on May 3. We celebrate 100 years of cinema on this date. Karan is very kicked about the film and that's why he called him to come and assist him.`