Kristen Stewart has poured her heart out about the late Diana, Princess of Wales ahead of portraying her in an upcoming film.

Spencer will depict the events of a weekend in the early 1990s, when Diana wrestled with her marriage to Prince Charles and decided it was failing.

With Kristen, 30, in the lead, she's had to throw herself head first into the role - reckoning the story is "one of the saddest to exist".

Production is scheduled for a January start date, while Kristen has her nose in books for her extensive research.

The star, who became a household name with the Twilight franchise, told InStyle : "The accent is intimidating as all hell because people know that voice, and it's so, so distinct and particular.

Kristen has revealed her feelings about Princess Diana's story (
Image:
Getty Images)

"I'm working on it now and already have my dialect coach. In terms of research, I've gotten through two and a half biographies, and I'm finishing all the material before I actually go make the movie.

"It's one of the saddest stories to exist ever, and I don't want to just play Diana - I want to know her implicitly. I haven't been this excited about playing a part, by the way, in so long."

Diana was killed in a horrific car crash in Paris in the early hours of August 31, 1997.

She had signed the divorce papers from Prince Charles the year before.

Diana sadly died in 1997, following a car collision (
Image:
BBC)
Diana and Charles signed their divorce papers in 1996 (
Image:
PA)

Kristen also recalled her struggle to publicly discuss her sexuality.

She continued: "The first time I ever dated a girl, I was immediately being asked if I was a lesbian.

"And it's like, 'God, I'm 21 years old.'"

Kristen shot to fame in the Noughties with Twilight and its sequels, starring opposite heartthrob and new Batman Robert Pattinson.

Kristen is taking on the huge role (
Image:
AFP/Getty Images)
Kristen and Robert dated in real life (
Image:
SUMMIT ENTERTAINMENT)

The onscreen love interests dated in real life, but following their split, Kristen has mainly been linked to women.

She was first linked with current girlfriend Dylan Meyer in August last year, a month after she seemingly split from Stella Maxwell.

"When I was dating a guy I was hiding everything that I did because everything personal felt like it was immediately trivialised, so I didn't like it," she told Elle at the time.

"We were turned into these characters and placed into this ridiculous comic book.

"And I was like, 'That's mine. You're making my relationship something that it's not.' I didn't like that."