Princess Kate's affordable birthday mini dress and knee-high boots combo was peak Y2K chic

Kate wearing cream knit in Nottingham
Kate briefly opened up on her cancer journey on Christmas Day (Getty)

On January 9, the Princess of Wales celebrates her 43rd birthday.

Since becoming a member of the British royal family, the Berkshire-born icon has become a style muse, with fashion fans and royal enthusiasts alike idolizing her sartorial agenda around the globe.

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Back in 2007 for her 25th birthday, six years after she first met the Prince of Wales during their University years at St Andrews, the-then Kate Middleton was spotted arriving at her home in west London - and her outfit proved she's been a fashion mogul ever since the 2000s.

Kate Middleton during Kate Middleton Sighting As She Arrives Home From Work - January 9, 2007 at Chelsea in London, Great Britain. (Photo by C. Uncle/FilmMagic)
Kate wore a Topshop dress for her 25th birthday (FilmMagic)

Kate stepped out oozing monochromatic cool in a black and white square neck dress from high street retailer Topshop. The piece featured intricate shell-style detailing and contrasting stripes across the neckline and the belt, creating interest without feeling overwhelming.

She paired it with suede black knee-high boots - a footwear style she's continued to champion. In her most recent outing for Christmas Day at Sandringham, she paired her go-to boots with a long emerald green coat dress and a 'symbol of bravery' scarf.

Kate layered her Y2K top shop dress with a single-breasted black blazer and accessorised with a black shoulder bag featuring a white trim.

Kate Middleton Sighting As She Arrives Home From Work - January 9, 2007 at Chelsea in London, Great Britain. (Photo by C. Uncle/FilmMagic)
Her look was the epitome of Y2K cool (FilmMagic)

The stylish royal's wardrobe is still peppered with accessories that possess a 2000s flair. In an official post on the Prince and Princess of Wales' Instagram, William shared a black and white portrait of Kate, wishing "the most incredible wife and mother," a happy birthday. "The strength you’ve shown over the last year has been remarkable," he continued, "George, Charlotte, Louis and I are so proud of you. Happy Birthday, Catherine. We love you."

To accessorise her laid-back 'jeans and a t-shirt' look Kate wore a checked scarf featuring a large gingham print and playful tassel trims.

"Gingham has been claimed as a Gen-Z staple in recent years," explains H! Fashion's Tania Leslau. "Beloved for its kitsch, colourful aesthetic, the beloved print originated in the 17th century and was initially imported to Europe from Southeast Asia."

The princess' birthday outfits prove her penchant for timeless style with an injection of trend-led flair.