The event marked the 100th anniversary of the world's oldest Air Force - the Royal Air Force - which was formed on April 1, 1918, independent of the British Army and Royal Navy. Following the service at Westminster, a royal flypast took place over Buckingham Palace.
The royal couple will meet both President Michael D Higgins and Taoiseach Leo Varadkar during their relatively short two-day trip. The former Suits star changed out of her Dior dress into a forest green top and buttoned midi pencil skirt ensemble by go-to designer Givenchy with suede camel pumps, structured Strathberry brown leather tote and a low side-part bun.
They will also visit a number of Dublin's main cultural attractions, including the Irish Emigration Museum, EPIC - where the Duchess will learn about her Irish ancestry.
When you become a member of the Royal Family there are certain fashion guidelines one is expected to abide by.