Meghan is believed to get on well with The Queen after accompanying Her Majesty on a series of engagements in Cheshire in June, where they were pictured laughing and smiling together.
The Queen has praised the Royal Air Force for its "tenacity, skill and gallantry" as she was joined by senior members of the royal family at the centrepiece of centenary events.
A day after gathering for the youngest royal heir's special church service, Prince William, Kate Middleton, Prince Harry, and Meghan Markle helped celebrate the 100th anniversary of the Royal Air Force.
Harry, the Duke of Sussex, also wore his No 1 RAF uniform, with RAF Regiment shoulder flashes, in recognition of Honington - the home of the RAF Regiment - and also for his role as Honorary Air Commandant of the base.
Prince Harry and Meghan Markle aren't your regular Duke and Duchess of Sussex. (Picture: AFP) The tribute to the RAF, which became the world's first independent air force when it was founded as a separate entity from the British Army and Royal Navy in 1918, began with a service at Westminster Abbey.
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He went on to explain how the current political turmoil in Britain will work to the EU's advantage in Brexit negotiations. But the mood in Brussels - especially after hearing this afternoon that Boris Johnson too was gone - is far from blasé.
A total of 17 royals flanked the Queen on the Buckingham Palace balcony for the RAF celebrations.
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.
Later today, Meghan and Harry will fly to Dublin where they'll spend the next two days.
The pair arrived at Dublin airport, with Harry wearing a green tie and former Hollywood actress Meghan in a dark green Givenchy dress that appeared to have been chosen with Ireland's national colour in mind.
In their biggest ever formation, 22 Typhoon jets spelt out the number 100 in the sky - an added surprise for the royals, personnel and the throngs of public spectators who had packed out the streets to watch.