The Princess of Wales always adheres to the unofficial royal fashion hemline rule. It's thought that royal ladies' dresses and skirts should finish at the knee or no higher than four inches above, maintaining modesty and giving a formal element to outfits.
Back in 2010, Prince William announced his engagement to Kate, sparking worldwide joy. Royal fans were so excited to finally see King Charles' eldest son's future bride make her public royal debut - but it was her engagement dress that really stole the show.
Take a look back at the now iconic outfit and find out why the future queen made history with her rule-breaking move...
© Getty
Kate glowed as she posed at St. James' Palace in 2010
Then known as Catherine Middleton, she was already known for her exquisite beauty, from her cascading mane of rich brunette curls to her megawatt smile, but this public appearance also showcased her fashion credentials.
© WireImageKate's dress was by Issa London
Kate chose to mark the momentous occasion by donning a UK brand, Issa London, which designed her glorious royal blue gown, which perfectly complemented her sapphire engagement ring that once belonged to Princess Diana.
© GettyKate's dress had wrap detailing and boasted a flippy hem
Cut in a striking wrap style, the elegant number featured a pleated front, flared skirt, and delicately ruched waist ties. The hemline was also a little shorter than the ones Kate would wear today. We've seen Kate wear slightly daring hemlines before during relaxed outings, but this was a public photocall at St. James' Palace.
© GettyThe dress was an instant sellout
The dress retailed at £430 at the time, and became a big hit, selling out in over 42 countries after the royal stepped out in it.
© GettyEveryone was entranced with Kate's royal blue dress
Daniella Helayel, the designer for the brand, previously reflected on the moment Kate wore the frock. "That morning I'd gone to yoga as usual, and then I got a call from a friend telling me about the royal engagement," she previously recalled to the Daily Mail. "It was all very exciting. We didn't have a TV at the studio, and this was pre-Instagram, but we soon knew Kate was wearing Issa because at four o'clock, the phones began ringing and didn't stop. It was bonkers."
Dressing for date night
© WireImageKate wore the same dress in purple in 2011, after she was married. It's also a perfect date night style. During a royal tour of Canada, the brunette royal opted for the same style by Issa, in another regal colour - deep purple.
On a visit to Ottawa, Kate accessorised the style with a simple clutch bag, high-heeled shoes and a Maple leaf brooch, borrowed from the late Queen Elizabeth II.
© WireImageAs a fashion editor who has been specialising in royal style for over eight years, I would say this is a great date-night dress. It's formal and elegant enough to wear to a fabulous restaurant, and the slightly flared skirt and subtle V-neck give it a fun, flirty, almost romantic feel.
I would style this timeless dress with a pair of high heels, a top-handled bag, and some statement, shoulder-grazing earrings. As Valentine's Day falls in chilly February, a chic trench coat could also be a welcome addition to layer over such a gorgeous dress for added warmth.
