Princess Diana (Emma Corrin) may be the breakout star of The Crown season 4, but her many, many costumes get a tight second billing. Costume designer Amy Roberts, who won an Emmy in September for her work on season 3, faithfully recreated—and reimagined—dozens of memorable looks from the royal's early years in the spotlight, from pre-wedding overalls and flashy ballgowns to, of course, the wedding dress that defined a generation.

“What do I remember? What do you think about? The sleeves, the bigness of that, and that huge, long, great train. That’s what I have to achieve,” Roberts says in a 10-minute behind-the-scenes costume featurette, exclusive to ELLE.com. The video dives into the making of the dress (it took 14 weeks and employed the same lace company that worked on Diana's real gown) and one of Corrin's five fittings.

“I remember the first one, I was like, ‘Should my mum be here?’ I was like, ‘This is such a… it is a wedding dress fitting. It might be the only one I do in my life,’” Corrin jokes.

The video also explores how Roberts captured Margaret Thatcher's “extraordinary, hugely feminine” style (“She was obsessed with clothes,” actress Gillian Anderson reveals of her character) and the emotional turmoil Roberts and director Jessica Hobbs wanted to convey for Helena Bonham Carter's Princess Margaret in episode 7, “The Hereditary Principle.”

“We just talked about this late-life bruising, what was happening to her,” Hobbs says. “It's just so beautiful when you go through the episode and realize what Amy's done… Suddenly all these colors appear, which are very like a bruise deepening over time.”

Bonham Carter puts it a bit simpler: “I’ve never spent more time on a job in costume. It was very much a collaboration. Although, Amy, a lot of the time, would say, ‘Just shut up and get on with it, you look marvelous.’”