On This Day in Royal History: Kate Middleton's Little Blue Dress

For the announcement of her engagement to Prince William, Kate Middleton arrived wearing a sapphire dress by one of her go-to labels, Issa. Designed by Daniella Issa Helayel, the blue dress, which featured long sleeves, a deep V, and ruched banding at the waist, was one of Helayel’s classic silhouettes. But when Middleton wore the royal blue number — which coordinated with Princess Diana's blue sapphire ring that William had used to propose — it became an instant hit and put Issa on the minds of fashion fans across the globe.

Hayel explained that she had no idea Middleton would choose one of her label's designs for the big reveal. Middleton had been a loyal customer since before the engagement, wearing Issa to events such as London Fashion Week.

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"We didn't have a TV at the studio and this was pre-Instagram, but we soon knew Kate was wearing Issa because at four o'clock the phones began ringing and didn't stop. It was bonkers," Hayel told Elle.

The design proved to be so popular that it sold out at Harvey Nichols within a day. Averyl Oates, the storied department store's buying director, told British Vogue, "The dress worn by Kate sold out almost immediately. Issa is one of our best-selling brands and the versatility of the pieces mean that they can be dressed down for the day and dressed up for special occasions." Even Tesco, a big-box store, sold a version of the dress that retailed for ￡16. Naturally, online orders sold out in a week and the dress sold out in stores within a week.

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The blue Issa dress didn't just make waves for fans of the royal family. Kate's blue period spread to the red carpet, too. According to the News-Times, nearly 100 celebrities chose blue dresses for events ranging from premieres to awards ceremonies in the wake of Middleton's big moment.

It wasn't all good news, however. While Middleton made Issa a household name, Hayel's brand wouldn't last.

"From the day of the royal engagement, our sales doubled," Hayel told Hello. "I didn't have the money to finance production on that scale."

In what many have called the Kate Effect, Issa couldn't keep up with the demand for the blue dress and Hayel eventually left the brand she'd built for over a decade. Not soon after, the line shuttered.

"I left because I couldn't take any more. I felt so stressed that my hair went white and started falling out. I was broken by the end of it," she told Elle. "I had a great business, which I'd built up on my own over a decade. To watch it evaporate was heartbreaking."

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Hayel has since moved on, establishing a new brand, Dhela. There's a dress that bears a striking resemblance to Middleton's LBD and it's safe to say it'll make any fan of Kate's style perfectly happy.