Kate Middleton's Go-To Designer for Princess Charlotte Launches U.S. Collection — See Her $110 Dress

Peter pan collars and handstitched smocking are the order of the day as one of Kate Middleton’s favorite childrenswear brands debuts in the U.S.

Pepa & Co, the London-based label, favored by Kate for her two children, Prince George and Princess Charlotte has just launched a pop-up store at Saks Fifth Avenue in their Miami, Florida, branch.

“We are very excited!” Pepa Gonzalez, managing director of Pepa & Co, tells PEOPLE, adding: “It’s a capsule collection so some pieces are from the current collection and some are exclusive as they from the spring collection.”

One piece in particular might prove popular. The blue dress worn by Princess Charlotte in Canada last year has been relaunched in white and is available as part of the Saks collection. The traditional design which retails for $110 features a frilled collar and red embroidered hand-smocking with a waist bow.

The blue and coral version sold out in less than 24 hours, when Charlotte wore it last September to a playdate at Government House in Victoria during Kate and Prince William’s royal tour of Canada.

Founded by Gonzalez four years ago, business has been booming since Kate discovered the Spanish label. Mostly sold online (although she has a showroom in London’s Hammersmith) one of their best-selling items was a $39 striped whale sweater that Prince George wore in official pictures to mark his third birthday.

Earlier this year, both royal siblings had starring roles at their aunt Pippa Middleton’s wedding where they wore head-to-toe bespoke Pepa & Co as page boy and flower girl at the nuptials.

Although London-based, the collections are manufactured in Spain and influenced by the designer’s Spanish heritage. “In Spain and at Pepa & Co, we believe in trying to keep the essence of timeless clothing for children and enjoy seeing our children look like children,” says Gonzalez.