After the service at the Abbey, the royals went to Buckingham Palace to watch a flypast of aircraft to mark the centenary celebrations.
The Duchess of Sussex's latest sartorial statement happened during a reception at Glencairn, the residence of British ambassador Robin Barnett, where she stepped out with Prince Harry in a belted black dress by Emilia Wickstead and stylish shoes from one of her favorite designers, Aquazzura.
She was unable to attend the christening of Prince Louis of Cambridge on Monday, as she was travelling, but paying homage to Britain's military services is one of her most important roles as monarch.
The royal couple with also meet with young people interested in coding when they visit the startup hub Dogpatch Labs in Dublin 1.
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.
The RAF, which is the first-ever independent air force, split from the British Army and Royal Navy in April 1918.
The Queen looked radiant in a royal blue silk coat with a turquoise collar over a dress in the same colour, both by Angela Kelly, with a matching hat and a diamond star.
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