Britain's Prince Harry poses with Meghan Markle in the Sunken Garden of Kensington Palace, London, Britain, November 27, 2017.

It seems as if everyone wants to know what Meghan Markle is wearing.

The 36-year-old American actress, who's set to marry Britian's Prince Harry on Saturday, has quickly morphed into a fashion icon. Nowadays, almost every time a photographer snaps a photo of her, the outfit she's wearing sells out, according to one observer.

Fashionistas have dubbed it the "Meghan effect."

"We've seen it again and again; anything she's worn sells out within hours," Josh Duboff, senior writer for Vanity Fair covering entertainment and culture, told CNBC.

"Brands have noted kind of immediate effects in terms of the influence she has, in terms of her bags, her clothes, her fashion, sunglasses she wears," Duboff told "Power Lunch" on Friday.

Stores "can't keep them in stock," he added.

The effect of the latest addition to the royal family is considerable. Brand Finance, a consultancy firm, estimates the royal wedding will boost the British economy by about one billion euros, or near $1.2 billion at Friday's exchange rates. Markle's fashion choices alone are expected to generate about $212 million in retail and apparel sales, the firm noted.

A camel-colored collar wrap, originally priced at $1,395, was worn by Markle on Christmas. Sentaler, the Canadian luxury outerwear brand, confirmed in an email to CNBC that the jacket "sold out instantly," after the actress appeared in photographs alongside her prince.