See the Princess of Wales in a similar outfit in 1989.
Embodying the late Princess of Wales, Stewart was spotted with her blonde hair perfectly coiffed and wearing a plaid red-and-green blazer, white turtleneck, black skirt and tights. Stewart also wore black Adidas as she roamed the set, as she was snapped putting on black sunglasses.
Spencer is set in December 1991, and focuses on three days of the princess' short life, as she faces the end of her marriage to Prince Charles while spending Christmas at Queen Elizabeth's Sandringham Estate in the 1990s.
Diana wore a similar outfit while on a visit to Portsmouth, U.K., on Jan. 23, 1989. Prince Harry and Prince William's mom was photographed with a plaid blazer with a black lapel, white turtleneck, pearl earrings and red clutch.
This is the second classic Diana look that people have seen. The first-look image was revealed late last month.
"Spencer is a dive inside an emotional imagining of who Diana was at a pivotal turning point in her life. It is a physical assertion of the sum of her parts, which starts with her given name; Spencer," Stewart said in a press release at the time. "It is a harrowing effort for her to return to herself, as Diana strives to hold onto what the name Spencer means to her."
Back in November, Stewart told ET about how she's preparing to play Diana.
"This is a really kind of poetic, really internalized imagining of maybe the heaviest three days’ time before she does something as gnarly as leaving the royal family," Stewart said. "I'm just sort of reading everything that I can and then forgetting it, because it's kind of a really internalized story."
The actress also previously admitted that she was finding Diana's accent "intimidating as all hell." "People know that voice, and it's so, so distinct and particular... I'm working on it now and already have my dialect coach," she said in an interview with InStyle.
For more on Stewart's role in Spencer, watch below.