Princess Diana's royal fashion rule that Princess Kate has never followed

We all know just how much the late Princess Diana was a total style icon and her outfits will go down in history. Her daughter-in-law, the Princess of Wales, has a similar effect on the public. Just like Diana, the world watches what she wears and she causes mass sellouts consistently.

But it's fair to say that Prince William and Harry's mother was a little more 'out there' with her fashion choices, even when she was married to King Charles.

Iconic fashion designer Dame Zandra Rhodes recently confirmed this very notion to Saga Magazine, revealing that Diana loved black dresses, especially as daywear, even though unofficially, royals should only wear black at funerals as it's essentially a colour of mourning.

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Dame Zandra explained: "She was very shy. She would come into my shop in Mayfair and go through the rails.

"Sometimes she picked something in black, which the royals weren't allowed to wear except at funerals, so we would make it in her size in a different colour.'

Meanwhile, daughter-in-law Kate never wears black to royal engagements other than during a period of mourning. The royal, who has a wardrobe full of rainbow-hued clothing and chic neutrals, always adheres to the unspoken rule.

Diana's most famous black frock was, of course, her standout 'revenge dress' by Christina Stambolian which she wore to the Serpentine Ball in 1994.

But she also rocked a black dress early on in her relationship with King Charles.

Back in 1981, when the pair were engaged, Diana wore a show-stopping black gown by David and Elizabeth Emanuel, who would later design her wedding dress, to a fundraising concert. It caused quite the stir! Many years later, Diana was interviewed for her biography in 1991, and reportedly said that when Charles saw her in the dress, he remarked: "Only people in mourning wear black!"

In 1990, Diana was pictured arriving at the Nottingham Medical Centre with her sons William and Harry. The trio were visiting the then Prince of Wales after an operation. Diana wore a stunning black Chanel dress for the occasion.

Well, they do say black is the most stylish shade one can wear!