The film, which will be directed by Karan Malhotra of "Agneepath" fame, earlier had Kareena Kapoor Khan and Hrithik Roshan as the lead pairs.
But the project derailed due to Hrithik's health issues, which forced Kareena to walk out of the film.
Then Salman Khan signed on the dotted lines to play the lead role in "Shuddhi" with his leading lady was still undecided. But Khan also oped out of the venture.
Johar took to Twitter to announce the film's leading cast.
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Even Salman has congratulated Varun for his new film.
"Kamaal karte ho Varun Dhawan... Made your dad and me so proud of you... Happy Shuddhi," he tweeted.
This will be Varun and Alia's third film together after "Student of the Year" and "Humpty Sharma Ki Dulhania".
"Shuddhi" is expected to hit theatres during Diwali next year.