Minutes after the designer was confirmed, her name was trending on Twitter and people rushed to the website to try and purchase the crêpe de chine, empire-line number, with many reports claiming that it was from the Jenny Packham spring/summer 2013 collection.
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However, a spokesperson for the brand confirmed that the dress was, in fact, a one-off creation for the new mum's long-awaited appearance outside the hospital.
Asked whether she had also made a pink version should the royal baby have been a girl Jenny answered, "I couldn't possibly comment."
It's not the first time that the royal has worn Jenny Packham – she's known for her love of the British designer's creations and has shown off her stunning gowns many times before.
During her North American tour back in 2011, Kate stepped off the plane in Calgary wearing their canary yellow sundress. And she cheered on her husband at the polo in Santa Barbara wearing one of her hand-painted floral frocks.
Just one month later, William and Kate made their debut public engagement as a married couple, attending the ARK gala with Kate wearing a dazzling pale pink Jenny Packham gown.
In May of last year, the Duchess stepped out at the Olympics gala swathed in a stunning teal floor-sweeping number by the brand.
She even incorporated Jenny Packham into her maternity style, accentuating her baby bump in a bespoke silk shantung coat and daisy lace dress to attend a special service marking the 60h anniversary of the Queen' coronation.