"Tomorrow you will be part of the audience forever Janhvi Kapoor cause your trailer comes out... Firstly, sorry I'm not there in Mumbai but I'm by your side, don't worry," Arjun tweeted on Sunday night.
"I just wanted you to know this profession is amazing if you work hard, be honest, learn to take the accolades with the brickbats, respect opinions, yet follow your own path and instinct. It's not gonna be easy, but I know you are ready for all the madness that will ensue," he added.
Arjun said that director Shashank Khaitan has presented Janhvi and Ishaan Khatter as the "modern Romeo and Juliet" in Dhadak.
Arjun is step-brother of Janhvi and her sister Khushi, daughters of his father Boney Kapoor with late actress Sridevi.