Tarun has closely worked with Karan on many projects like Kuch Kuch Hota Hai, Kabhi Khushi Kabhi Gham and Kabhi Alvida Na Kehna.
Recently, the news of Dostana 2 going on floors at the end of this year was also a buzz. Tarun, thus has his hands full with both these projects.
Sources close to the film share that Karan was 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 so that the movie comes out great."