Kate Middleton transformed appearance to be more 'appropriate' before engagement

Over time, Kate Middleton has transformed her style in keeping with her role as future Queen, going from 'the girl next door' to a bona fide style icon whose fashion is followed around the world

Prince William and Kate Middleton dated for around 10 years before announcing their engagement - and during that time, she underwent a transformation in order to be a more 'appropriate' future Princess, according to some royal experts.

The couple famously met as first-year students at the University of St. Andrews in 2001; by 2003 they were officially a couple, and apart from a brief break-up in 2007, they were together until William popped the question in 2010. Public interest in Kate first exploded in 2004 when she and William were papped enjoying a ski trip together. And when the Middleton family attended William's passing out parade at the Royal Military Academy Sandhurst in 2006, rumours of an engagement started to mount.

As their relationship grew more serious, it's thought Kate intentionally evolved her style, swapping spaghetti straps, low-cut jeans, and deep V necklines for tailored coats, long-sleeved tea dresses, and structured suiting. As one expert noted: "Kate's fashion sense changed rapidly as she adjusted to life in the royal spotlight, going from girl next door to elegant future Queen."

Certainly, her future as William's wife seemed cemented at William's passing out parade in 2006. Royal journalist Rebecca English said on the Channel 5 documentary William and Kate: Too Good to Be True that "We hadn't expected Kate and her family to turn up, and myself and a number of photographers and journalists were all standing on a press stand together. Suddenly, out of the corner of [our] eye, we saw Kate and her mother and father being ushered down to the front of the seating. I remember turning to the person next to me and saying, 'That's it. It’s a done deal. This woman is going to be our future Queen.'"

English added: "Suddenly, the engagement whispers were starting. There was intense pressure on William and Kate, and, short of printing the tea towels, everyone had these two walking down the aisle imminently." With a proposal from her handsome Prince on the cards, Kate started to focus on her image - and her royal future.

"Her clothing almost began to reflect what people saw in her character - a kind of restraint, kind of modesty almost," royal author Tom Quinn said in that same Channel 5 documentary. “I think that did come about because William and Kate were coming towards the point where they would announce their engagement. It was Kate starting to behave in ways which would be seen more appropriate for a future Queen.”

Then, on November 16, 2010, William and Kate's engagement was finally announced. She stepped out in a blue Issa wrap dress, looking every inch a princess - and the 'Kate effect' was born. Today, Kate is considered one of the world's most iconic stylish women. Whether wearing recycled outfits, high street items or beautiful gowns, her looks have a huge impact on trends and sales, with her endorsement recently estimated to be worth £1bn annually to the fashion industry, according to Newsweek.