Farah, 49, gave the 'Chennai Express' actress her first break in Bollywood seven years ago with the romantic reincarnation film 'Om Shanti Om'.
"She has really grown as an actress. She was a rough diamond when she started her career in 2007 but in these seven years I feel she has become a polished diamond. She is like my kohinoor," Farah said during the promotion of her upcoming directorial venture 'Happy New Year' in the capital.
Though Deepika has improved as a performer, Farah feels she is still the same for her.
"She has not changed as a human being for me. We are still like mother and daughter. I feel the equation never changes with family no matter how big you become," she added.
Deepika plays the role of a bar dancer Mohini Joshi in 'Happy New Year', which also stars Shah Rukh Khan, Sonu Sood, Abhishek Bachchan, Boman Irani and Vivaan Shah.
Asked who is the best dancer among the lot, Farah joked, "Vivaan was the best and happy dancer in the film because he never tried to learn steps and did whatever he felt like during the shooting."
The film, which will release on October 24, is a story of a team of six losers participating in a dance competition in their attempt to pull off the greatest diamond heist ever.
"I feel this is the biggest and toughest film of my career. We had fun during the shooting of the film. It was tough to make them shoot together because they were busy in their own pranks," Farah said.

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