Cerise Coat, Cherry Blossom Dress and Rachel Trevor Morgan Hat

This cerise crepe coat, silk dress with a cherry blossom pattern on an ivory background and cerise straw hat by Rachel Trevor Morgan with upturned brim trimmed with silk flowers (peonies?) made its first appearance during the Queen's most recent visit to Australia, on 25 October 2011, when she officially opened the new Royal Children's Hospital in Melbourne, paired with the City of London Lily brooch:

I love how the nurses' pink uniforms match the Queen's outfit!

 

On 4 July 2012, the Queen selected this outfit, together with the Australian Hibiscus brooch, to attend a service of thanksgiving to mark her Diamond Jubilee at Glasgow Cathedral:

After a couple of years under the radar, this outfit reappeared for a garden party for the Household Cavalry at Buckingham Palace on 28 May 2014. The Queen and the Duke of Edinburgh were accompanied by the Princess Royal and Prince Harry. The Guards' badge was worn:

 

This outfit seems to have become a sort of garden party staple, as the Queen repeated it on 10 May 2016 for her first Buckingham Palace garden party of the season, accessorized with the Flame Lily brooch and one of her trademark clear umbrellas against the London rain (Daily Mail article here):

 

The Queen wore the dress on its own on 1 June 2016, to meet Joachim Gauck, the President of the Federal Republic of Germany, at Buckingham Palace (itv article here). As it's sadly quite common with this type of engagement, it's impossible to tell exactly which brooch HM is wearing: