Ever since “The Crown,” Season 4, bowed on Netflix, the stylesphere has been filled with strange declarations of desire for the pie-crust collars, novelty sweaters, puffed-sleeve floral frocks and 1980s power jackets immortalized by Princess Diana as she ascended to stardom and Princess Anne as she issued caustic asides. Followed pretty much immediately by queries on how to “get the look.”

Such fantasies are rarely easy to fulfill, involving, as they would, time travel — or at least fruitless searching through the pages of Vogues British or American and the social media posts of influencers. But this time around there is actually an answer.

It lies in a house in Fitzroy Square in Central London, where Chiara Menage, an elegant 54-year-old former film producer, runs an online vintage clothing store from her kitchen table: Menage Modern Vintage. She is the only employee, and until Amy Roberts, the costume designer for “The Crown,” discovered her trove of 1970s, ’80s and ’90s garments, she was pretty much an undiscovered treasure. (She still has only 807 followers on Instagram.)

But the Peter Pan-collared floral Liberty print dress Diana wears when Prince Charles issues his ill-fated marriage proposal? Menage Modern Vintage. The pale yellow puff-sleeve midi-skirt suit Diana wears for her lunch meeting with Camilla? Hardy Amies from Menage Modern Vintage. The red power suit Diana wears on the way to the Christmas finale? Valentino, Menage Modern Vintage.

All of which means the shop and its founder are about to get thrust into the royal spotlight. In the meantime, Ms. Menage agreed to tiptoe out of the shadows to reveal some of her secrets over Zoom.

How did you become the ultimate royal fashion resource?

I spent 20 years working in independent movies and then had three boys, took some time and wanted a change. I’d always loved clothes, but I haven’t bought anything new since about 2000. I live near Marylebone, which is a quite rich area, and I started shopping in charity shops and discovered people were throwing away beautiful Givenchy outfits that I’d never be able to afford to buy new.

I think it’s much easier to find a piece you love by accident than to go into a shop like Selfridges with a list. If you go into a charity shop, something just jumps out at you and insists you have it. Later I got much more interested in the sustainability side of things. I just don’t understand why you would ever buy anything new. Underwear aside.

So I had accumulated a lot. Then about two years ago a friend’s daughter said, “Why not set up a website?” My friends also said they had loads of clothes they didn’t know what to do with, and I thought, “Why not?” I just blithely set it up. I had no idea what I was doing.

What is “modern vintage”?

Vintage is officially anything over 20 years old. The millennium is a useful benchmark. Now a lot of people try to cash in on the word and say “vintage” in a listing when it’s clearly not.

I started with a rainbow-sequined catsuit by Rifat Ozbek, one of only two ever made — the other belonging to Grace Jones — that was given to me after a shoot for one of his videos. I did a lot of partying in that suit, but it had been gathering dust in the attic. It was one of the first things I sold, to a collector, and it gave me the money to create a small studio in my basement with a borrowed camera and other things I needed for the business. It also taught me a lot about letting go. This business is not going to make me rich, but I have met a lot of interesting people because of it.

Like who?

I had a client who was a princess. I met Sandy Powell, the costume designer, during lockdown because she was home for the first time in ages. She had a big clear-out and gave me 60 pieces, so we decided to sell everything to benefit Refuge, the charity, because we both felt we had been very lucky, all things considered.

I met a young woman on a Photoshop course who said, “My granny’s gone, will you help me clear out her clothes?” Then she took me to her granny’s home, which turned out to be a stately home in the country with a whole floor of clothes from the 1950s. A lot ended up in “The Crown.” Now the young woman sends me messages saying how amazed she is her granny’s stuff is being worn by Princess Anne.

Speaking of “The Crown,” how did that happen?

Through a mutual friend, who brought in Amy Roberts, the costume designer. I had just taken on five huge storage units of clothes, sight unseen. They were from a woman, an heiress, who had died and been a complete shopaholic and hoarder. She would stay in a hotel, do a load of shopping at places like Balenciaga and Hermès, nick all the hotel toiletries and then buy a Louis Vuitton suitcase to put everything in. It took months to go through it all.

We found some suitcases full of 12-year-old smoked salmon. Bills from the Dorchester for 14 million pounds. The clothes were pristine. Most hadn’t been worn. So Amy came to have a look and then said she was going to set aside a whole day to come back with her assistant, who is also her daughter. She ended up coming three times and took between 80 and 100 pieces.

Are there pieces in the show you think are particularly special?

There are loads I love! I just did a post about a floral silk two-piece pajama set by Ungaro. “The Crown” put it on someone in Mustique. I thought, “I really want it back,” but I don’t have the lifestyle, and it didn’t fit. There was a suit made by Arabella Pollen that was big white and green stripes, and I was really glad because Arabella used to make clothes for Princess Diana, and that one really said it all.

The red Valentino suit Diana wears I had actually sold to someone in Italy and hadn’t shipped yet, and then Amy saw it, and I had to call the buyer up and ask if we could keep it after all. It’s lovely seeing the pieces being worn in actual scenes.

Any tips on what is coming?

A friend of mine recently told me about being invited to a 21st birthday party at Windsor Castle in the early ’80s. She borrowed a dress from her sister — Bellville Sassoon, black velvet, backless with boned bodice and huge skirt. It turned out to be identical to the one Diana was wearing at the party.

The next day the tabloids went crazy with the headline “Mystery blonde upstages Diana” and camped outside her house for a couple of weeks after bribing a dastardly Etonian to reveal her identity. They offered her the princely sum of 1,000 pounds to pose in the dress getting into a taxi at night, which she refused. She is digging out the dress and the press cuttings from the attic, and I hope to offer it soon.