Ms Stewart addressed the upcoming release during an appearance on Jimmy Kimmel Live where the Twilight star admitted she felt “protective” of the late Princess.
She said: “I didn’t grow up with her maybe in the same way, I was really young when she passed away.
“I feel sort of the same way about her. It happened really quickly.
“It’s hard not to feel protective of her. She was so young.
“I mean, everyone’s perspective is different and there’s no way to get anything right because what is fact in relation to personal experience.”
According to royal expert Robert Jobson, the production is set to ruffle royal feathers, especially if the script does not correlate to real life scenarios.
Mr Jobson told Us Weekly: “They won’t like it, but they would have expected it.”