Lincolnshire's RAF Red Arrows and the Battle of Britain Memorial Flight Lancaster will fly over Buckingham Palace for the flypast at 1pm.
The dress features an nearly identical open-shoulder neckline as her Givenchy wedding gown, and has a strikingly similar silhouette.
For the occasion, the Suits alum wore a bespoke dark navy Dior dress that featured a boatneck and full skirt.
Other female members of the royal family that donned badges included the Duchess of Cornwall, Princess Anne and Sophie, Countess of Wessex. Kate Middleton went with an icy blue dress by her go-to designer, Alexander McQueen, and a hat by Sean Barrett.
Prince Louis gained six new godparents during his christening at St James's Palace yesterday, with the service containing two lessons, two hymns and two anthems.
Both dresses feature a similar boat neckline and silhouette.
Prince Harry and Meghan visit Republic of Ireland
Other royal family members present today include the Queen, Prince Charles and the Duchess of Cornwall. She's accessorised with a decorative hat by Stephen Jones , a chic clutch and pale heels.
The pair met the Taoiseach of Ireland Leo Varadkar as they arrived at Government Buildings in Dublin.
The Queen, 92, was front and centre for the RAF events.
(Picture: Getty) Heir to the throne Prince Charles and his wife Camilla, his son Prince William and wife Kate, and Prince Harry and his wife Meghan, all joined the queen on the palace balcony for the display.
After a busy week in Scotland last week, the queen faced another busy week ahead in London, including a meeting with visiting President Donald Trump and first lady Melania Trump on Friday.
The anniversary brought the royal fab four together again.
It was 100 years ago on April 1 1918 that the Royal Flying Corps and the Royal Naval Air Service merged to create the RAF - the world's first independent air service.
The flypast was a centrepiece of events celebrating the RAF's centenary, with lines of invited personnel given a prime viewing position directly outside the palace gates.
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- Meghan and Harry join the Queen at RAF centenary service