Kristen Stewart has spoken about getting a “sign-off” from Diana, Princess of Wales for her performance in the biopic Spencer, recently premiered to considerable acclaim at the Venice and Telluride film festivals.

In an interview with the LA Times after the film’s North American premiere at Telluride, Stewart said she had some “spooky, spiritual feelings making this movie”, which takes place over three days during the 1991 Christmas break, when Diana was staying at Sandringham house. “Even if I was just fantasising. I felt like there were moments where I kind of got the sign-off.”

Stewart added: “[Diana] felt so alive to me when I was making this movie, even if it’s all between the ears and it was just a fantasy of mine. But there were moments where my body and mind would forget she was dead.”

“It was … a fight to keep her alive every day, and so remembering that she was dead was just absolutely lacerating. It just destroyed me constantly. And that itself felt spiritual … there were times where I was like, ‘Oh, God,’ almost like she was, you know, trying to break through. It was weird. And amazing. I’ve never felt anything like it in my life.”

Spencer, directed by Chilean film-maker Pablo Larraìn, has been widely praised since its world premiere at the Venice film festival on Friday. In a five star review, the Guardian’s Xan Brooks called it “rich and intoxicating and altogether magnificent”, while the Daily Telegraph, in another five-star review, described it as “thrillingly gutsy, seductive, uninhibited film-making”.

After its Venice screening, Stewart told a press conference of her admiration for and empathy with Diana, saying: “We haven’t had many of those people throughout history. Diana stands out just as a sparkly house on fire.”