Actress Dakota Johnson was forced to keep her casting in the upcoming Fifty Shades Of Grey film adaptation a secret from her famous parents Melanie Griffith and Don Johnson for weeks, because she feared they would accidentally leak the big news.

The star offspring reveals she got the call she would play Anastasia Steele while shooting another movie in New York last summer (13), but she couldn't celebrate the news with her loved ones.

She tells America's Elle magazine, "Sometimes your parents are the ones with the biggest mouths of all time."

Instead, an emotional Johnson, who had been staying at a friend's house, burst into tears of joy and toasted her achievement with a strong drink.

She says, "I was just crying, and there were all these dogs in the house. This one dog was below my feet sleeping, and I was like, 'You f**ker, wake up, this is really exciting' - and then I had a glass of whiskey."

Johnson will star opposite Jamie Dornan as Christian Grey in the raunchy movie, based on the erotic series by E.L. James.