Speaking with The Hollywood Reporter for their Drama Actress Roundtable, the 31-year-old star was asked whether she connected with her character as they both spent their 20s "under a microscope" by the media.
"It seems like the clearest parallel," explained the actor, "there were a lot of cameras in our lives — but the reason they were there is so different.
"I’m not running from anything; I’m running toward everything. This person [Diana] wasn’t even allowed to be a person. So I know what it’s like to assume — sometimes wrongly — that everyone’s looking at you when you walk into a room.
"I can relate to being like, 'Oh, I’m going to go to the bathroom right now, and I wonder if anyone’s going to walk in there after me.' But it’s only the small sort of weird stuff that I can relate to."
While Stewart was first brought into the limelight because of her leading role in the Twilight saga, in Spencer she plays Diana in 1991, spending three days with the Windsors and coming to the decision to split from Charles.
Director Pablo Larraín explained the movie to her as “a poetic sort of fever dream” which gave the actress some freedom in terms of how to portray the iconic princess.
The fact that Diana lived in such an isolated world, also meant that Stewart did not have the chance to talk to any of the people who knew her and were close to her, although she acknowledged that plenty of memoirs were available.
She shared that the cast "watched all the documentaries and read all the memoirs", but found that there were many contradictory accounts to assemble.
However, she explained that the film was "a tone poem, versus something kind of educational, so we kind of couldn’t do anything wrong”.
Watch: Kristen Stewart says she doesn't care about the Oscar buzz surrounding her performance in Spencer.