The Kate Effect runs in the royal family.

Princess Charlotte posed for her birthday portrait in a John Lewis cardigan – and the adorable knit is already sold out.

Kensington Palace released the portrait taken by the Duchess of Cambridge on Monday, a day ahead of the little princess’s second birthday.  And the pastel yellow John Lewis Baby Luxury Sheep Cardigan adorned with a Fair Isle print and fluffy blue sheep that Charlotte wears is no longer available on the retailer’s site. It originally ran for $23. You can still snag a pink coordinating dress in some sizes marked down to just $13.50 on the John Lewis site – for now.  The designer hasn’t responded to requests for comment yet.

Looks like Charlotte has inherited the same golden touch as her mother. Almost anything Kate Middleton wears sells out faster than you can say “your highness,” which has been dubbed “The Kate Effect” or “The Cambridge Effect.” Some analysts estimate her influence is worth nearly $2 billion in the U.K. fashion industry alone.  Part of the appeal is that she’s got timeless taste, and she’s a master of mixing classic upscale designs from Jenny Packham and Burberry with affordable pieces from places like TopShop. So it’s no surprise that the pieces she swaddles Prince George and Princess Charlotte in have also become must-haves.

When the 10-hour-old Charlotte was photographed with her parents in May 2015 wearing an $88 G.H. Hurt & Sons shawl, it began selling like crazy in just minutes, with 100,000 people from more than 183 countries crashing the site. And parents went gaga over the pink knit cardigan with white ruffled collar that she wore for her first birthday portrait last year.

“We were thrilled when Princess Charlotte was photographed wearing our Rose Stitch Cardigan in her official first birthday pictures,” Emma Davison, co-founder of Olivier Baby & Kids, told the Telegraph.  “As a young British brand we were honored that the Duchess of Cambridge chose to dress her daughter in our clothes. She has such fabulous style. It is a huge compliment.”

It’s estimated that Princess Charlotte’s influence will pump more than $4 billion into the U.K. economy over her lifetime, experts at Brand Finance predict. And that’s a billion dollars more than the Prince George Effect.

And all eyes will be on what dress the little royal wears when she’s the flower girl at her aunt Pippa Middleton’s wedding on May 20.