Kate Middleton's $70 Zara dress is already sold out

On Sunday afternoon, Kate Middleton wore a $69.90 blue summer dress from budget retailer Zara. By Sunday evening, the dress was sold out.

Several fans lamented on Twitter about not being able to buy the highly-coveted garment.

KATE MIDDLETON LOVES TO COOK THIS ONE DISH

Though true fans should not be surprised that an outfit Middleton wore instantly sold out. The “Kate effect," as it has been called, is not uncommon to the Duchess of Cambridge – for whom the phenomenon is named.

The mom of three wore the blue and white striped mid-length dress while she was on an outing with her two older children, Prince George and Princess Charlotte, to watch Prince William compete for the Maserati Royal Charity Polo Trophy at the Beaufort Polo Club.

The Duchess paired the belted frock with neutral-toned wedges.

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Though Middleton was praised for her fashion sense – the mom was ridiculed on Twitter for allowing her son, Prince George, to play with a toy gun during the outing.

Her sister-in-law Meghan Markle also experienced some Twitter backlash over the weekend for wearing an off-the-shoulder blush dress to the Queen’s birthday parade.

Alexandra Deabler is a Lifestyle writer and editor for Fox News.