It would not be possible to talk of the royal influence on fashion, and indeed society, without mentioning Princess Diana.

The world watched the evolution of a fashion icon, the one who went from 'girl next door' who bagged a prince, to original wearer of the 'revenge dress.'

Diana's style changed drastically in the years after she came into the royal fold.

Each decade a different fashion feel – some trends are revived and recreated diligently year after year on the catwalks. The pencil skirt or the cat-eye sunglasses of the 50s, for example.

Whilst others – the psychedelic prints or vinyl white knee-high boots from the 1960s – are now reserved for fancy dress.

Diana's style is markedly different in the 80s and 90s. By the time of her tragic death, long gone were the high-neck pussy-bow blouses and instead, she was wearing closely-cut dresses showing décolletage.

Anya Hindmarch, the designer, told the Telegraph, "We used to laugh when we designed what she called her 'cleavage bags,' little satin clutches which she would cover her cleavage with when she stepped out of cars."

There is no such thing as 'throw on and go' if you're a royal; each outfit was a carefully-managed show, giving the world exactly what Diana wanted it to see.

The 'Lady Di' blouse – pale chiffon with a satin necktie by David Emmanuel (the designer who would go onto create her wedding dress) epitomised English-rose. Diana wore it for a feature on young beauties for Vogue, shot by Lord Snowdon, hitting the newsstands on the very day her engagement to Prince Charles was announced. PR perfection!

It was copied over and over by retailers, dupes selling in their millions in the coming days.

From these humble beginnings, Diana's clothes soon became a lesson in sartorial style, often turning decades of royal tradition on its head.

None are as symbolic as that 'revenge dress' – the LBD she wore to the Serpentine Gallery's summer party, hosted by Vanity Fair in 1994.

When it was first shown to Diana by designer Christina Stambolian, she was said to be concerned it was 'too daring.' And so her decision to wear it shows a deliberate departure from the old Diana. She wore it on the same night that a controversial interview with Prince Charles aired on ITV.

When interviewer Jonathan Dimbleby asked Prince Charles if he had been faithful to Diana throughout their marriage, the Prince said yes, before adding: “Until it became irretrievably broken down, us both having tried.”

The comment was taken as an admission of Prince Charles’s infidelity and since then, that Serpentine gown has been known as the 'revenge dress.'

Commentators are quick to asses the similarities between Princess Diana and Meghan Markle.

Both are known as humanitarians. Princess Diana helped reduce the stigma around Aids and campaigned on landmines.

She once said: "I would like to be a queen in the hearts of the people."

Royal fashion etiquette states that women should usually wear gloves when greeting members of the public; but Diana liked to hold hands with the people she met. Images of the Princess touching Aids victims had a significant impact on changing the public perception of the disease.

The difference between the Princess and the soon-to-be Duchess being, of course, that Diana's humanitarian work largely came following her exit from the Royal family.

Meghan used her fame prior to becoming a royal to champion causes, such as women's rights. Now she must find a way to continue her humanitarian work whilst taking on a royal role.

She will no longer be able to air her thoughts on politics and she will have to go through royal protocol before being interviewed.