A few celebrities took to Twitter to share their wishes for the filmmaker. Here's what they said:
Genelia D'Souza: Happy birthday @kjohar25 lots and lots of love and love today and always.
Kabir Bedi: @kjohar25 Happy Birthday, Karan! Yash would be so proud of all you've achieved! Wishing you decades of fulfillment.
Manish Malhotra: @kjohar25 Happy birthday my dearest friend.
Bipasha Basu: Happy Happy Birthday @kjohar25. Love your spirit! Looking forward to the most amazing and anticipated party in a long time. I love birthdays! Big hug!
Divya Dutta: @kjohar25 A very happy birthday Karan! Big hug and god bless.
Riteish Deshmukh: Wishing my dearest friend @kjohar25 a very happy birthday. Thank you for always being there for me - LOVE YOU LOADS.
Ronit Roy: @kjohar25 Wish you a very happy birthday and a life filled with all the love and luck in the world!
Farah Khan (Jewellery designer): Happy Birthday Karan. Wish you a super 40th year with loads of love luck and success. Let's parttttttaaaaaaaayyyyy tonight???
Johar, son of late filmmaker Yash Johar, made his debut as a director with 1998 hit 'Kuch Kuch Hota Hai'.
He also helmed films like 'Kabhi Khushi Kabhie Gham', 'Kal Ho Naa Ho', 'Kabhi Alvida Naa Kehna' and 'My Name Is Khan', and produced others like 'Dostana', 'Kurbaan' and 'Wake Up Sid', through which he gave new directors their golden chance.
Johar is one of the most loved filmmakers in the Hindi film industry, given his cheerful attitude, wit and charm. No wonder most industry members are kicked about his grand birthday party at a suburban hotel.
Karan is busy working on his next directorial titled 'Student Of The Year'.