The Windsor's won't love Lucy Cohu's portrayal of one of their own, she tells Emma Pomfret..
As the modern British monarchy's original wild child and its first media star, the antics of Princess Margaret were never far from the gossip pages during her lifetime.
In fact, the story of Margaret's spectacular fall from grace was ripe for dramatisation, according to director Simon Cellan-Jones - and that's exactly what Channel 4 has done in its controversial £2 million royal romp, The Queen's Sister.
"When I got the role everybody had a terrible Princess Margaret story to tell me, they made her out to be an absolute monster, but truly there were three sides to her - the princess, the film star and the showgirl," smiles actress Lucy Cohu.
Single mum Lucy - who stars as the the late princess alongside Toby Stephens as Margaret's photographer husband Anthony Armstrong-Jones and Shameless star David Threlfall as the Duke of Edinburgh - says that her portrayal of the princess wasn't intended to be salacious or contrived, but to explore the reasons behind her behaviour.
"I think that people will be able to relate to her - everybody has felt lonely and has had painful relationships or has behaved in a way that they shouldn't have, especially in their younger life," she explains.
"Certainly in mine, I know that I sort of hurled myself from situation to situation without really thinking about the consequences, and I think that in Princess Margaret's position, it would be a thousand times worse because there was nobody around to say, 'What are you doing?'.
"There were a lot of people who deferred to her all the time but when they got tired of her I can only imagine that it exacerbated her sense of isolation. I have great empathy for her," Lucy adds.
Indeed, Margaret's life was a constant battle as she attempted to dispense with the formalities of her privileged position while instinctively crushing anybody who didn't treat her with the deference she thought she deserved, according to the 35-year-old actress.
"The character of Margaret took me completely by surprise - this complicated, sad, tragic, funny, childlike person," she reveals.
The drama begins in the 1950s, when the late Princess was Britain's most glamorous star, and ends with a tragic portrait of the Mustique-era Margaret. Lucy is clearly over the moon to be starring in a film about perhaps one of the most vilified royals of the last century.
"I believe I was actually the first person they saw - when I read the script I laughed a lot," she beams.
"I didn't really know much about Margaret's life before filming, except for the scandal surrounding Townsend when she first met him, and what was going on in her later years, of course.
"The whole concept of being a royal and behaving in a royal way seemed strange to me - after all they're just human beings with titles and money."
Lucy admits that perfecting the part of the Queen's younger sister was a huge challenge, not least because of the time constraints.
"I had so much work to do on such a tight schedule. We had a four to five week shoot to do the whole film. Margaret is in every scene apart from one," she says, adding that she also sang all of the songs herself.
"It was pretty gruelling at times. Some days I was 45 years old in the morning, in the 1960s in the afternoon, and 25 years old at the end of the day.
"Then there was the hair, the contact lenses and the nails, and having to play younger and then play older. I knew I didn't look particularly gorgeous wearing prosthetics but after a while I didn't care that I didn't look particularly great with two chicken fillets and a big saggy neck!" Lucy laughs.
The Queen's Sister has already stirred up a huge amount of controversy, with Lord Snowdon, now 75, reportedly 'incandescent with rage' - and the film hasn't even been aired yet.
"I didn't expect the media furore at all," reveals Lucy. "It was really bizarre. We've had months of speculation about the sex scenes and all that, but it's really not about that, it's more about human nature.
"Also, people have to remember that we're not doing a drama documentary here - it's a drama based on her life - but it is a drama all the same," she explains.
"Of course there will be people who think that it's outrageous and I think I can understand that but I do hope that when they see it they'll see that it's very affectionate."
The end of the film portrays the twilight of Margaret's life and is a time for reflection rather than sorrow.
"The thing that I really felt about playing her was that she was down but she was never defeated," says Lucy. "I felt that the end of the film was quite positive in a way, as it implied that there was the possibility of new beginnings, having taken on and having been through this extraordinary life.
"Maybe it was finally a chance for peace. I'd hope so because there is always another way, even when you feel there isn't."
* The Queen's Sister is on Channel 4 on Sunday, November 27.