Kristen Stewart on what she learned researching Princess Diana for her role in Spencer

Kristen Stewart has described Princess Diana as “one of the most unknowable people in history”.

The 31-year-old actress will portray the late Princess of Wales in the upcoming drama ‘Spencer' and she has opened up on the amount of research she did to get an understanding of her role.

She told Entertainment Weekly: “There are contradictory materials from the horse's mouth.

“She doesn't always say the same thing in every interview, you know? There was a fickle nature, obviously, to a lot of the facts.

“She is, very sadly and very ironically, one of the most unknowable people in history, when all she wanted was to just be closer to people and bare herself.”

Kristen acknowledged not everyone will think she's perfected her performance, but she's confident she's tackled the role in the right way.

She added: “There was something just in absorbing her completely over the last six months leading up to this.

“I knew that I had hit some kind of elemental energy. If people have a lot to say about it not being a perfect impression, that's so okay with me.”

While the ‘Twilight' star was just seven years old with Diana died in a car accident in 1997, she had no doubts about accepting the part.

She explained: “I knew even before I read the script. I was like, ‘You're not going to say no to this, because who would you be in that case?'

“I absolutely would have felt like such a coward. Especially given that I'm such an outsider. I'm not from the UK, I don't have any particular investment in the royal family.

“So I was kind of this really clean slate, and then could absorb her in a way that actually felt very instinctive, you know?”

Meanwhile, Kristen recently suggested the spirit of Diana gave her a “sign-off” for her performance.

Asked whether she had ever had a paranormal encounter, she said: “No. But I felt some spooky, spiritual feelings making this movie.

“Even if I was just fantasising. I felt like there were moments where I kind of got the sign-off.”