Princess Kate's rule-breaking sheer dress she could never wear now

Demure and elegance are the pillarstones of the Princess of Wales' wardrobe today, but she has not always been so conservative with her fashion choices.

Before marrying Prince William in 2011, the mother-of-three often pushed the boundaries with her wardrobe – take her sheer dress at St Andrews University's fashion show runway and her silky slip dresses for nights out with Pippa Middleton for example.

One outfit we hadn't spotted before was her sheer black mini dress from September 2007, just weeks after the couple reconciled following their three-month split. William's then-girlfriend was spotted leaving London with a suitcase and a handbag – perhaps to visit the royal during his British Army training.

Kate did not look dressed for a long journey, donning a little black dress with mini puff sleeves, a square neckline and a fitted waist leading to a broderie Anglais skirt. As she walked away from the camera, the sheer back of her frock came into view, showing off her delicate bra straps.

She completed her look with white ballet pumps that matched her handbag, layered silver bangles that snaked up her wrist and her hair styled in soft waves that accentuated her layers.

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Kate and William's split

The couple became close friends while studying at the University of St Andrews in 2001. While living together in their second year, their relationship turned romantic, but it wasn't made public until they were spotted holidaying at Klosters Ski Resort in Switzerland in 2004.

"When I first met Kate, I knew there was something very special about her, and then I knew there was possibly something I wanted to explore there, but we ended up being friends for a while," Prince William explained during their 2010 engagement interview with ITV's Tom Bradby.

After graduating from university in 2005, the Prince joined the Royal Military Academy Sandhurst (RMAS) and worked his way up from an Officer Cadet to a British Army officer before joining the Household Cavalry (Blues and Royals) where he became lieutenant.

William broke up with Kate in April 2007 via a phone call, but they reunited two months later.

"I at the time wasn't very happy about it, but actually it made me a stronger person," Kate recalled. "You find out things about yourself that maybe you hadn't realised – I think you can get quite consumed by a relationship when you're younger – and I really valued that time for me, as well."

William also reflected on their time apart, musing that it made them stronger. "We did split up for a bit, but that was just, we were both very young, it was at university, and we were both sort of defining ourselves as such and being different characters and stuff.

"It was very much trying to find our own way and we were growing up."

During their split, Kate showed off her It-girl wardrobe, from her satin strappy dress with a low neckline for a night out at Mahiki in London in 2007, to a green sequin halter-neck top and yellow shorts for a charity roller disco party in 2008.

Since 2011, when she married Prince William at Westminster Abbey, Kate has refined her wardrobe to include power suits and long hemlines, turning to designers such as Alexander McQueen, Reiss and L.K.Bennett.

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