For the Royal Variety performance on Wednesday, the Princess of Wales wore a new-to-us Talbot Runhof dress. Talbot Runhof is the design collaboration between Adrian Runhof (a German) and Johnny Talbot (an American). It was interesting that Kate didn’t go with a repeat, and it looks like this gown has been in her closet for years, because the designers confirmed that they had no idea she owned this and it’s a few years old. The designers sounded happy about it, even though “the Kate Effect” is struggling pretty hard these days, with so many of Kate’s favorite labels going out of business or dramatically downsizing.

Kate Middleton’s latest red carpet moment was two years in the making, but the designers behind her velvet green dress only got a quick heads-up! Adrian Runhof — co-founder and designer at Talbot Runhof, the brand behind the Princess of Wales’ outfit choice for the Royal Variety Performance on Nov. 19 — tells PEOPLE exclusively that the palace notified them that she’d be wearing their dress about 30 minutes before the royal’s appearance.

“Two hours later, our name and our dress have been posted worldwide, so we are very thankful to her,” he says. “We think she is great, we respect her and it’s a great honor for us that she picked this dress, that she obviously liked it enough to buy it and select it for the event last night.”

Runhof — whose celebrity fans include Selena Gomez, Helen Mirren and Oprah Winfrey — explains that the classic dress has been in their collection for many seasons, and he believes that Princess Kate, 43, purchased it through a department store.

“I think she bought it a few seasons ago and found it in her wardrobe and thought, ‘Why don’t I wear this? It’s so beautiful,’ ” he tells PEOPLE, adding that Kate looked “impeccable.”

The designer adds, “We focus on making beautiful dresses, that’s what we do. I think the dress spoke to her. I doubt she knows who we even are, but she fell in love with it, and maybe that’s how it should be.”

Runhof says the “secret” to their dresses is their feminine and flattering fit, adding that there was an extra bonus to Princess Kate’s choice. “The best thing is that it’s a wonderful stretch velvet, so it feels as comfortable as a pair of pajamas!” he explains.

Twenty-five years ago, American Johnny Talbot and German Runhof started the brand, quickly discovered by Georgio Beverly Hills, a store that used to exist in Los Angeles that was a popular spot for celebrities hitting the red carpet.

The Princess of Wales’ dress choice may hint that she’s considering the brand for the upcoming state visit to the U.K. by German President Frank-Walter Steinmeier and first lady Frau Elke Büdenbender. “We are very excited to hear about it when it happens,” Runhof tells PEOPLE, adding that the German first lady owns many of their dresses. “She might be wearing one when she comes to the U.K. in December, too!”

[From People]

The Telegraph also devoted an article to glazing Kate for her “pre-diplomatic dressing” by choosing a German designer, all because of the upcoming state visit by Chancellor Steinmeier. The Telegraph also bizarrely claims that this dress is “no longer available to buy, indicating just how far in advance the Princess and her team plans for these engagements.” Does anyone actually think that Kate purchased this dress two years ago and thought “this will be good for the 2025 Royal Variety show?” No. Kate used to shop and shop and shop and she has a closet full of clothes she’s never worn. And that’s probably why it feels like her clothing allowance has been cut so dramatically in the past two years as well, and why she tried to make a big deal about how her office would no longer talk about her fashion.

Photos courtesy of Avalon Red, Cover Images.