The Twilight star took on a royal challenge for Spencer, which follows Princess Diana over the course of a pivotal weekend in her life: December 1991, when she decides to leave her husband, Prince Charles.
Though the movie only focuses on a small portion of time, the Best Actress nominee spent four months researching the late royal.
“The script doesn’t profess to know anything, it doesn’t cover any black-and-white detail,” Stewart told Variety. “But I read everything. And somehow, in a sort of abstract way, the script substantiated everything I learned in detail. So it was really nice that The Crown existed. And it was really nice that we’ve had all these documentaries and this evolved relationship with what happened.”
To take on Diana’s voice, Stewart worked with dialect coach William Conacher, who also trained Emma Corrin for The Crown and Naomi Watts when she played the People’s Princess in 2013’s Diana.
For the physical transformation, hair and makeup designer Wakana Yoshihara created two wigs, each costing close to $6,000, to capture Diana’s feathered bob.
“This process took about six weeks, and I probably colored the wig three times before I met Kristen,” Yoshihara shared with InStyle. “When we did the first fitting I knew the color wasn’t right, so I colored it again.”