Anticipation has reached levels not seen since the 2011 wedding of Harry's brother Prince William and Catherine Middleton, who in the end wore a white and ivory satin gown designed by Sarah Burton from the Alexander McQueen fashion house, a 100 percent British creation. 

US actress Meghan may also opt for a dress from her adopted country to curry favour with the public and to boost Britain's valuable fashion industry.

There is also some speculation, although far less, about what ex-army man Harry will wear on his big day -- a civilian suit or a full dress uniform?

Read also: Meghan Markle: LA actress with the fairytale role

Whimsical, traditional, or both? 

London has been buzzing for weeks with rumours about who will design Markle's dress, with Burberry, Ralph & Russo, who had made Markle's engagement dress, Stella McCartney, Erdem, Alexander McQueen, Antonio Berardi and Roland Mouret all being mentioned.

Mouret told AFP in February that he wouldn't reveal if he was the chosen man, saying: "She's a friend and the great gift I can give my friends is to keep their lives private." 

Fashionista Markle told Glamour magazine in 2016 that her ideal  outfit would be "very pared down and relaxed."

"I personally prefer wedding dresses that are whimsical or subtly romantic," she said.

But by marrying into the royal family, Meghan is also joining an institution whose traditions will  impose their own restrictions.

"From Honiton lace to Orange Blossom, Royal Wedding Dresses over the years have encompassed tradition, whilst still embracing changing fashions," the family's official website said of its approach to the gown.

British Fashion Council chief Caroline Rush believes Markle will strike the right balance.

"Throughout the past couple of months, Meghan Markle has proved to be very considered in her choice of what she wears," she said.

"She understands the subtle power fashion has in terms of challenging conventions, connecting to a community but also putting local companies in the spotlight."

Meghan's previous marriage to film producer Trevor Engelson also throws up a complication, raising the question of whether she will be able to wear white.

"The etiquette on white dresses for second marriages is now very fluid," wedding dress designer Raishma told the Daily Express.

"However, she is marrying a member of the Royal family, so she may opt for ivory or an off white shade which actually would be perfect on her skin tone."

Read also: Dior reveals making of Song Hye-kyo’s wedding dress

International exposure 

One thing for certain is that the designer will receive a worldwide boost from the exposure that only a royal wedding can provide.

The ceremony will be beamed into homes across the globe, with the audience expected to be at least tens of millions.

Moments after it is first unveiled, the dress will be analysed from every possible angle by websites who provide links for those looking to recreate the wardrobes of the famous.

But it is not only Meghan's choices that will affect the fashion world.

"The royals have been influencers long before the term even existed," explained Sam Coates, a PR expert based in London.

"No matter what your thoughts on the royal family, they can certainly propel a brand to fame."

Markle and the Duchess of Cambridge have both chosen to wear high-street brands in the past, heralding a shift in the industry.

"These accessibly priced pieces sell out in seconds," he said. "My view is that this is a great opportunity, for both emerging and established brands to gain exposure on an international level."

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