Runway 34 trailer launch: Ajay Devgn reveals the BIGGEST difference between co-starring with Amitabh Bachchan and directing him for the first time

Ajay Devgn and Amitabh Bachchan have costarred in six movies prior to Runway 34 (not counting the latter's cameo in Bol Bachchan). So, BollywoodLife quizzed the former on the difference between sharing screen space with legend and directing him.