Kristen Stewart shares her 'favourite' titbit about Princess Diana

The 31-year-old actress will play the late royal, who died in a car crash in 1997 at the age of 36, in Pablo Larrain's biographical drama, reports femalefirst.co.uk.

She said: "Even when she looked her most beautiful and most substantial, she also felt like she could kick her shoes off and walk outside with you, ask how you are, and you would feel that honesty from her. It's hard to do that when you are teetering around on heels and looking like no one can come near you.

"We do see that as beautiful but she was really able to be there; she was so present -- that's my favorite thing about her."

The movie takes place a few days over Christmas 1991 at Queen Elizabeth's Sandringham Estate, as Diana, who was born Diana Frances Spencer, decides to end her marriage to Prince Charles.

Stewart said there were royal advisers around on the Motion Pictures' set to ensure the film remained "authentic", and she learned to curtsy while shooting the movie.

"We had royal advisers, we had people to tell us all the things that you couldn't know as an outsider. The stage that we depict in the film is a true unraveling," she added.

"So, once I learned the curtsy and I learned that we are supposed not to go in the kitchen ourselves and steal food, all of those details, I don't really remember them, but there was always someone around to make sure that if anything was out of line that we were remaining authentic and we weren't undermining what we were trying to do, because obviously, I'm American and not from that country."

The actress also said the script won't come as a big shock.

Speaking at the Venice Film Festival, she added: "The movie doesn't offer any new information. It doesn't profess to know anything."