Providing intel on what the film will cover, she revealed that Spencer, named after Diana's maiden name, "will take place over three days, and it's this really poetic internal imagining of what that might have felt like rather than giving new information. We sort of don't have a mark to hit. We just also love her."
According to Deadline, the official description of the film describes it as being about a weekend in the '90s where Diana knew her marriage to Prince Charles wasn't going to work out and she quickly had to develop her own path.
In October, Stewart delved into her process on becoming Princess Diana, from her history to her accent.
"The accent is intimidating as all hell because people know that voice, and it's so, so distinct and particular,” the Twilight actor revealed.
“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."
She added, "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."
Fascinated? You can check out Kristen Stewart's full interview here.