Kate Middleton’s Velvet Dress Designer Reveals They Only Got a 30-Minute Heads Up on Red Carpet Moment (Exclusive)

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!”

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Fashion news and features director at The Telegraph, Bethan Holt, tells PEOPLE that Princess Kate looked “amazing” in the Talbot Runhof dress.

“It was quite a daring look from her, which I think shows how confident and happy she is right now,” Holt shares, adding that it was reminiscent of another stylish royal.

“It was very [Princess] Diana,” she says. “The neckline really echoed Diana’s revenge dress, albeit a slightly more demure version. Diana also had a penchant for sumptuous velvets and that slinky body-skimming silhouette. This gown felt like a nod to that.”