Earlier on Tuesday, the pair attended a service at Westminster Abbey to mark the centenary for the Royal Air Force (RAF), which included a flypast of around 100 aircraft. Harry was suitably dressed in a suit and also had a green tie.
Auntie Meghan kitted herself out in a sophisticated Ralph Lauren dress for the christening of Prince Louis yesterday - and even dug out matching heels and a hat.
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".
The choice of Ireland for Prince Harry and Meghan Markle's first official foreign trip holds special significance given the impact of Brexit on the Irish border and the Queen's focus on strengthening British-Irish relations.
"I think it looks very smart".
The head of the Royal Air Force, air chief marshal Sir Stephen Hillier, said that it is a "hugely important day" and the "pinnacle" of the centenary celebrations.
As well as being Britain's top defense system in air, the RAF has prevented conflicts and delivered aid in areas hit by natural disasters over the last many decades.
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.
Serena Williams vs Camila Giorgi, Wimbledon 2018
Despite the two-year gap since their previous meeting, Williams professed to having watched 52nd-ranked Giorgi play "a lot". It is the first time in Wimbledon history not one of the top 10 women's seeds have reached the quarter-finals.
Dead, Dozens Missing as Tourist Boat Sinks in Thailand
Television broadcast images of dozens of divers searching for the missing, while more rescuers waited on standby at a pier nearby. Some 48 people - passengers and crew - were rescued and one body found Thursday before the operation was suspended overnight.