We have to say, we think the new royal's minimalist look was strikingly similar to the famous black dress that Audrey Hepburn wore in her movie Sabrina.
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.
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.
The Duchess of Sussex, who will travel to Dublin Tuesday evening with Prince Harry, paired the dark navy dress with a matching fascinator by Stephen Jones, gold-and-diamond Cartier earrings, and, like her sister-in-law, nude pumps.
A trio of F-35B Lightning II aircraft of 617 Squadron taking part in the RAF100 flypast over London to mark the centenary of the RAF.
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The service will be followed by a fly-by at Buckingham Palace and another balcony appearance from the royal family.
On Wednesday, their day will start with an official meeting with Michael Higgins, the president of Ireland, before heading to Croke Park, where they will view an exhibit that includes artifacts from the Bloody Sunday massacre.
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.
Fresh from Prince Louis's christening yesterday, the royal foursome arrived at the iconic landmark for a service celebrating the RAF's history.
Markle wearing a Dior gown at a ceremony before the flypast of Royal Air Force aircraft pass over.
The occasion concluded with 22 Typhoons spelling out "100" as they flew over Buckingham Palace, and then the Red Arrows flew over London.