Karan is backing the film, an adaptation of the acclaimed Marathi film "Sairat", through his banner Dharma Productions.
"The journey of 'Dhadak' begins today! Janhvi and Ishaan, Shashank Khaitan (director of the film)," Karan tweeted on Friday.
Karan also shared an image in which the lead pair is seen sitting against the railing as they face their backs to the camera. Janhvi is wearing a vibrant pink hued ensemble and Ishaan in a blue kurta.
"Dhadak" is being shot in Udaipur as the film has Rajasthan as the backdrop. Sridevi has also joined Janhvi on the sets of her first movie.
While "Dhadak" will mark Janhvi's foray into Bollywood, Ishaan is making his acting debut with Iranian filmmaker Majid Majidi's India-set movie "Beyond The Clouds".
Ishaan's brother and actor Shahid Kapoor also took to Twitter to post: "...And when did he grow up. Didn't even realise."
"Dhadak" is scheduled to release in July next year.