In yet another demonstration of the 'Kate-effect', the fushia Jolene dress by British maternity label Seraphine is now in hot demand.
Fans stormed the website overnight in the hope of achieving the same glamorous look as the Duchess, and two hours after the news came out at midnight, the dress had sold out.
There is now said to be a four-week waiting list for the flattering knot dress, which has sold out in every colour, with pre-orders growing by the minute.
"We heard rumours online that an official royal family photo was going to be released imminently, so we were on the look out to see what her next outfit would be, and hoped it would be Seraphine, said Ceceile Reinaud, founder of the label.
"We saw the pictures go live online overnight and are absolutely honored and so happy to see her in another one of our dresses."
It's not the first time new mum Kate has chosen Seraphine. She was seen shopping in the brand's Renata polka dot dress when she was still pregnant, and chose to wear the Jolene dress in a floral print when she left Kensington Palace en route to Buckleberry with William and their new arrival.
HELLO! Online recently spoke to founder Cecile about the effect Kate's royal stamp of approval has had on the brand.
"The Kate effect is huge and we have been enjoying a 400% growth in sales since it became public that Kate bought Seraphine dresses back in April 2013," she said.
"A few weeks ago she was photographed wearing our Renata Spotty dress whilst shopping on King's Road and our sales boomed immediately with the dress completely selling out.
"Subsequently, our customers have put themselves on a four week waiting list to get hold of one!"
The company has also released figures that show sales of the knotted dress in particular have seen a 300 per cent boost.
Speaking about Kate's maternity style, Cecile added, "Kate has managed to stay true to her feminine and chic style during pregnancy. She has loved a bit of polka dot and soft prints and has continued to wow us with her stunning figure and legs by opting for slightly shorter hemline and accentuating her empire line."