Kajol is a must have for filmmaker Karan Johar in all his films because he feels his close friend is lucky for him. No wonder the actress features in a cameo in the song "Disco deewane" in Johar's forthcoming film "Student of The Year" (SOTY).

"Kajol is in the disco song and she has danced with the boys (Siddharth Malhotra and Varun Dhawan). Kajol's presence is very important for me. She has been there in every film of mine and she has always been lucky, " the 40-year-old said here.

Having Kajol in his films is almost like tradition, he says, adding: "I don't like breaking tradition, I am a creature of habit."

Johar's directorial debut "Kuch Kuch Hota Hai" also featured Kajol, who was also seen in his other projects like "Kabhi Khushi Kabhie Gham" and "My Name Is Khan". She also made a cameo in the song "Rock n roll soniye" from "Kabhi Alvida Naa Kehna".

The two male actors of SOTY were impressed with the actress when they shot with her for "Disco deewane", a new age version of the famous 1980s hit by Nazia Hassan.

"It was great, she just came on the sets, picked up the steps in 10 to 15 minutes, while we had been learning the steps for seven days. We actually felt for the first time, the star power, " Siddharth said.

"Basically when she was on the set no one saw us. We were like dancers, everyone was like 'Kajol ma'am is coming', " added Varun, son of filmmaker David Dhawan.