The director of racy movie Fifty Shades of Grey said she tells her children it is “a love story they’ll never see”.

Film-maker and artist Sam Taylor-Johnson described the erotic romance story as “a dark fairy tale”.

The film, based on the book by E.L. James and expected to hit screens in time for Valentine’s Day 2015, tells the story of billionaire Christian Grey who has a passionate relationship with student Anastasia Steele.

The director said: “It’s like the world of the Grimm Brothers. I like the transition of this girl and the journey that she goes on ... I hope I haven’t said too much.”

The movie was due to be unveiled in August, but was put back until 2015 having been dogged by difficulties with casting.

The production delay was thought to have been partly as a result of the abrupt exit of star Charlie Hunnam, who left citing his busy schedule and family commitments. He has now been replaced by Jamie Dornan from Northern Ireland.

Dakota Johnson has taken on the role of Steele.

Last month it was announced that James’s trilogy has sold 100 million copies worldwide. The series – dubbed ‘mummy porn’ – is fast becoming one of the most widely-read book series.