The Duchess of Sussex put on a stunning display as she joined the royals on the balcony of Buckingham Palace.

Meghan, who later flew to Dublin with Prince Harry, stunned in an elegant black Dior dress for a service commemorating the 100th anniversary of the Royal Air Force before joining the Queen to watch a spectacular fly-past.

Up to 100 jets, helicopters and planes from across a range of different eras of RAF history roared over central London today much to the delight of the thousands who gathered to watch the spectacle from below, according to the Daily Mail.

Britain's Queen Elizabeth II and Meghan the Duchess of Sussex watch a flypast of Royal Air Force (RAF) aircraft pass over Buckingham Palace in London. Photo / AP
Britain's Queen Elizabeth II and Meghan the Duchess of Sussex watch a flypast of Royal Air Force (RAF) aircraft pass over Buckingham Palace in London. Photo / AP

The Duchess, 36, paired the fitted and flared dress with a navy headpiece from milliner Stephen Jones, just hours after dividing fans in olive green Ralph Lauren at Prince Louis' christening at St James' Palace.

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She wore her tresses in an elegant side bun, which celebrity hair stylist Jason Collier says is a "sleeker and more elegant" take on what is fast becoming her signature look.

This morning's service marked the start of a busy day for Harry and Meghan, who were subsequently whisked off to Buckingham Palace and later flew to Ireland to kick-start their first overseas engagement since tying the knot.

Commenting on Meghan's dress, celebrity stylist and designer Lucas Armitage (the-timeless.com) told MailOnline that Meghan had made a "bold choice" by choosing black.

He added: "The boat neck and cut is reminiscent of the wedding gown so it's a silhouette she knows wows."

Meghan, the Duchess of Sussex, leaves after a service at Westminster Abbey to mark the centenary of the Royal Air Force, in London. Photo / AP
Meghan, the Duchess of Sussex, leaves after a service at Westminster Abbey to mark the centenary of the Royal Air Force, in London. Photo / AP

Based on the cut and style of Meghan's elegant bateau-neck frock, royal watchers were convinced it was a bespoke piece by her wedding dress designer, Clare Waight Keller of Givenchy, however it was later revealed as Dior.

Harry and Meghan were joined this morning by the Queen, Prince Charles and Camilla, the Duchess of Cornwall, and the Duke and Duchess of Cambridge, with Kate putting in a rare appearance during her maternity leave.

Also in attendance were Prince Andrew, Prince Edward and Sophie, the Countess of Wessex, Princess Anne, and Prince Michael of Kent.

Collier told MailOnline: "The bun is quickly becoming the Duchess's signature look, so it's no surprise to see her sporting this style at today's ceremony.

"It's clearly a style that she feels comfortable with, which is so important when you're stepping out in front of the cameras.

Prince William, The Duke of Cambridge, Catherine, Duchess of Cambridge, Prince Harry, Duke of Sussex, Meghan Markle, Duchess of Sussex and Queen Elizabeth. Photo / AP
Prince William, The Duke of Cambridge, Catherine, Duchess of Cambridge, Prince Harry, Duke of Sussex, Meghan Markle, Duchess of Sussex and Queen Elizabeth. Photo / AP

"Going back to the bun is a step away from the more casual low ponytail she sported yesterday, but as that was more of a private family occasion, perhaps she felt comfortable enough to try something new – today is a day for a tried-and-trusted look that she knows will photograph well.

"Meghan is known for wearing her hair in a looser and more relaxed style, but her hair today is much sleeker and more elegant, with a very tight ballerina-style knot in place of her usual messy bun.

"It's a sophisticated update on the look, ideal for such a formal occasion. I like that she's still given such a classic look a contemporary twist, by wearing the bun to the side, rather than in the middle of her head.

"This look also shows the neckline of her dress beautifully; she clearly likes the combination of a bateau neckline, a fascinator and an up 'do'. All three work together beautifully and it's a combination that looks fantastic, so I think it's safe to say this won't be the last time we see this look on Meghan."

Prince William, left, and from left, Kate the Duchess of Cambridge, Prince Harry and Meghan the Duchess of Sussex attend a ceremonial event. Photo / AP
Prince William, left, and from left, Kate the Duchess of Cambridge, Prince Harry and Meghan the Duchess of Sussex attend a ceremonial event. Photo / AP

This year marks the centenary of the Royal Air Force – the world's first independent air force – which was founded on 1 April 1918, independent of the British Army and Royal Navy.

For 100 years the RAF has defended the skies of Britain, preventing conflicts, delivering aid and combating cyber threats while working in partnership with other services.

These include Operation Ruman – the UK's humanitarian assistance operation in the aftermath of hurricane Irma which hit the Caribbean in September 2017 – and the RAF's Quick Reaction Alert Typhoon Aircraft, providing a UK air defence capability 24 hours a day, 365 days a year.

Today, the RAF is engaged on some 13 missions across 26 countries and is heavily committed on operations both at home and abroad.

 Prince William, The Duke of Cambridge, Catherine, Duchess of Cambridge, Prince Harry, Duke of Sussex, Meghan Markle, Duchess of Sussex. Photo / AP
Prince William, The Duke of Cambridge, Catherine, Duchess of Cambridge, Prince Harry, Duke of Sussex, Meghan Markle, Duchess of Sussex. Photo / AP

To mark its centenary year, special events, activities and other initiatives at local, regional and national levels will run from April to the end of September 2018.

The centrepiece of RAF100 is today, with a service in Westminster Abbey, followed by a parade in The Mall and spectacular flypast over Buckingham Palace.

Harry and Meghan later joined royals at a Buckingham Palace reception to mark the centenary of the Royal Air Force.

The couple met RAF servicemen and women, charity representatives involved in the RAF100 Appeal, RAF Veterans and Civil Service personnel involved in the Centenary celebrations.

Britain's Kate, the Duchess of Cambridge, Prince William, the Duke of Cambridge, Meghan, the Duchess of Sussex and Prince Harry, the Duke of Sussex, from second left. Photo / AP
Britain's Kate, the Duchess of Cambridge, Prince William, the Duke of Cambridge, Meghan, the Duchess of Sussex and Prince Harry, the Duke of Sussex, from second left. Photo / AP

In Ireland they will spend their time visiting organisations which are "central to Irish life", including the home of Gaelic football and the country's most famous university.

The couple will also attend a garden party at the British ambassador's residence, and attend official meetings with the Irish president, Michael Higgins, and Prime Minister Leo Varadkar.