The day began with a special service in Westminster Abbey, and was highlighted by a flyover of 100 aircraft, including Spitfires from WWII, above Buckingham Palace, with the royal family and a crowd of an estimated 70,000 in attendance.
Meghan, Duchess of Sussex joined Prince Harry, Duke of Sussex, Queen Elizabeth, the Duke and Duchess of Cambridge, Prince Charles and Duchess Camilla at the RAF Centenary where they all attended a Royal Air Force Westminster Abbey service.
"The forest green was a subtle nod to Ireland but it would be nice to see her adopt an Irish designer into her fashion roster over the course of her two-day stay".
Collier told MailOnline: "The bun is quickly becoming the Duchess's signature look, so it's no surprise to see her sporting this style at today's ceremony".
Harry was then seen laughing as he responded to his wife, while Meghan did her best to hide a smirk from her face.
In the hilarious clip, The Duchess of Cambridge did not look impressed as she turned around to face her husband and caught him sniggering in the middle of the Westminster Abbey service, trying to hide his amused expression.
Markle's third outfit choice was the Emilia Wickstead dress which she wore with simple black heels to the garden party reception at the British Ambassador's residence in Dublin.
Tuesday was a busy day for the royal family as they honored the 100 anniversary of the Royal Air Force.
Queen Elizabeth watched on today as nearly 100 aircraft flew over Buckingham Palace in a celebration to mark the 100th anniversary of Britain's Royal Air Force.
"Presenting the Royal Air Force with a new Queen's Colour provides an opportunity to congratulate the service for your remarkable contribution to defence over the last 100 years", she said.
After arriving at Dublin City Airport, Harry and Meghan were due to meet with Irish Prime Minister Leo Varadkar.