Kate Middleton's royal fashion a cash king for designers

Designers keep cashing in on the fashion sense of the Duchess of Cambridge and the Duchess of Sussex.

On Thursday, Kensington Palace released photos of Princess Charlotte's first day of school on social media.   Immediately the fashion industry noticed the red floral dress the Duchess of Cambridge was wearing. 

The $238 “Carnation Dress” by Michael Kors is already sold out online in what style spectators have referred to as the "Kate effect" -- nearly everything she wears in public sells out almost immediately.  Michael Kors representatives had not yet responded to inquiries from Fox Business at the time of publication.

High end designers aren't the only ones getting a bump in business from the Royal family. When Duchess Kate wore frocks from Zara and Topshop last year, they sold out within minutes.  Some savvy shoppers are now scooping up the apparel early and selling for a major profit on eBay.  Bloggers are even cashing in with sites like "Kate's Closet" linking to the Duchess'  designer looks as well as look-a-like alternatives when they sell out.

Much like her sister-in-law, the Duchess of Sussex, formerly known as Meghan Markle, is also known to drive designer sales thorugh the roof.

The website for a Canadian brand called Line The Label reportedly crashed after she wore a white duster coat for her official engagement announcment to Prince Harry in 2017.

Britain's Prince Harry and his fiancée US actress Meghan Markle pose for a photograph in the Sunken Garden at Kensington Palace in west London on November 27, 2017, following the announcement of their engagement. - Britain's Prince Harry will marry h

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While Middleton's wardrobe is fresh off the runway, she's been known to repeat outfits every so often. The Michael Kors dress she was just seen wearing was the same one she reportedly wore to Markel’s wedding rehearsal dinner last year. In 2013, Middleton wore a black-and-cream Temperly London dress for the third time to an event at the Natural History Museum.

US Weekly previously reported the royal wore the gown in Jan. 2012 to the premiere of “War Horse,” and to an event at St. Andrews University in Nov. 2012.