Kristen Stewart says Prince William, Prince Harry, and Diana were like a ’three-headed animal’

• Kristen Stewart said Diana and her sons William and Harry were like a "three-headed animal."
• Stewart plays the princess in the upcoming film "Spencer," and said she "absorbed" her character.
• When she was with her kids, Stewart said Diana was "unconditionally herself."

Kristen Stewart said Princess Diana, Prince William, and Prince Harry were similar to a "three-headed animal" in an interview with Entertainment Tonight.

31-year-old Stewart, who plays the Princess of Wales in Pablo Larraín's upcoming biopic "Spencer," told entertainment reporter Lauren Zima the part of her character she had to work hardest to perfect on-screen was Diana's close relationship with her sons and her experience of motherhood.

"The whole thing about watching her, within that space when her children are close to her, it's a nucleus," she said. "It's a three-headed animal, sort of an unstoppable beast."

Stewart doesn't have children but in preparing to play Diana on-screen alongside co-stars Jack Nielen and Freddie Spry, who were cast as William and Harry, she said she knew that "you don't want to mess with moms, you just don't do that."

Stewart told Entertainment Tonight that in her view, Diana "feels so embodied and so unconditionally herself when she is with her kids."

"In all of the research, that I was like, 'Man, that is what we are protecting here,'" she added.

When asked what it was like portraying a parent when she's not one, Stewart said being a "kid of a parent" did help her in some ways to understand the complexities of the relationship. "I do know what it feels like, that exchange. I can't say with certainty that I know what it feels like to be a mother," she said.

Later in the interview, the former Twilight lead said she feels like she "absorbed" Diana through the experience of filming "Spencer." Her comments echo those she made during an interview with Charlotte Higgins for The Guardian, published on Friday.

While she said she doesn't believe in ghosts, Stewart told Higgins she believes in "a lingering energy." When it came to portraying the late Princess of Wales, she added: "I took her in, whether or not it was my idea of her or there was some actual literal remnant of her."

"I guess it sounds kooky to start talking about stuff like this. But there wasn't a day that went by that I wasn't like: 'What does she think about this? I wonder if she can see me?'" Stewart added.

"Spencer" premieres in theaters on November 5.