Let’s start with the hair. Not Diana’s youthful riff on the Farah Fawcett flicks, but the ’90s post-divorce crop. Natasha Richardson’s haircut as Elizabeth James definitely gave a picture of the late princess as reference to her hair stylist.

“Her hair is beyond chic, healthy and shiny, and frames her face to perfection,” Bruhn says. “An important lesson can be learned here. Throwing on a wrinkled button-down shirt and jean with worn-out shoes and hair in a messy ponytail will not create a look for you that is similar to Princess Diana’s ‘off-duty’ style. If you want to understand why, study a photo of her wearing this look.”

When we first meet Richardson as Elizabeth James, not only does she have the Diana hair, but she is wearing a shift dress — a Diana staple for public appearances.

But why is it that such seemingly simple style choices remain so chic and memorable? “Part of the answer to this question is that it is not the actual piece of clothing being worn, but the woman wearing it — how she carries herself, how she takes care of the clothes she wearing, her posture, personality, and demeanor,” Bruhn says.

Why does an unfitted oversized white jacket look amazing on both of these women? Whatever the reason, Richardson and Diana carried it off with aplomb. “Another reason classic dressing appeals and goes beyond feeling safe: It is associated with the most glamorous women of the past living beautiful lives in movies, on yachts, in far away places, and at elegant cocktail soirées,” Bruhn says. “Audrey Hepburn, Jackie Kennedy, Carolyn Bissette, Grace Kelly, and Princess Diana are legendary for their beauty and exquisite taste, and yet they were actually wearing very understated clothing.”

Princess Diana’s Versace coat was indicative of her becoming more adventurous with fashion post-divorce, whilst James uses hers as a light cover-up whilst taking Annie on a trip around London.

Throughout the film, James sports a neutral palette, with an enviable selection of beige and cream tops. As she is getting ready to leave (read: panicking) and meet ex-husband Nick Parker for the first time in 11 years, she’s aptly wearing a safari shirt, ready for her holiday. Diana had a similar color palette and shirt selection on a trip to Egypt with Prince Charles in 1992.

Once again, these understated color palettes could easily veer into boring, but on these two timeless style icons, they don’t. “Each item [...] can either look stunning or completely blah,” Bruhn says. “The twist is that the simpler the garment, the more important the fabric and quality becomes.”

The epitome of laid-back-yet-put-together-ease, the loose button-down shirt has become a go-to for off-duty royals since Diana first rocked them. “Her shirt is pressed and her makeup is minimal, but gives her a natural glow,” Bruhn says. “That is the secret to classic dressing. It is a style aesthetic that can be completely underwhelming and down right frumpy, or with a little effort, can be super elegant and discreetly sexy as well.”

Elizabeth James’ relaxed vibe in Napa Valley is very similar and a far throw from her more buttoned-up style choices in London.

“If I was seeing my ex, after 11 years, and I had your legs, I’d wear this little baby,” James’ butler Martin says, holding the slinky black dress. “You'll kill it.” And kill it she does.

The LBD was a well-known signature of Diana’s in her post-Prince Charles years, with the late royal opting for designs from Versace, Catherine Walker, and others. “A sleeveless little black dress with a boat neck that shows off the collarbone and toned arms with a heel, there is truly nothing more chic than that,” says Bruhn.