The Queen sported a special diamond-encrusted brooch as she attended a reception marking the bravery of Canadian service people in the First World War.
The Queen wore a white gold and diamond sweetheart brooch, fashioned in the shape of the cap badge of The Calgary Highlanders for whom she is Colonel-in-Chief.
The brooch was a sweetheart token created especially for her by the regiment who are among a trio of Canadian military units who are on a European pilgrimage to mark the centenary of the 2nd Battle of Ypres, specifically the Battle of Saint Julien and Kitcheners Wood.
She was joined by the Duke of Edinburgh and Princess Alexandra, along with descendants of those of who fought in battle and current service personnel, at a reception at Canada House in Trafalgar Square, in honour of the three Canadian regiments which the royal members individually lead as Colonels-in-Chief.
It formed one of the highlights of events marking the centenary of First World War battles which are being commemorated by the trio of regiments, according to Canada's High Commissioner Gordon Campbell.
The Queen posed for a photograph with The Calgary Highlanders while Prince Philip sat for a portrait with The Royal Hamilton Light Infantry and Princess Alexandra joined the Canadian Scottish Regiment (Princess Mary's).
The Second Battle of Ypres was the first time Germany used chemical weapons on a large scale on the Western Front in the First World War.
Mr Campbell said: " It is always exceptional when Her Majesty comes and joins us at Canada House, particularly now as this is the 100 year anniversary of the bestowing of the first military honours to Canadians.
"You can just feel, in the room, how important it is to everyone that she is here. It is really an honour and it is the sort of commemorative activity that is important to the soldiers and the service people who are involved."
Honorary Colonel Richard Talbot, of the Canadian Scottish Regiment, said: "To have the three royal Colonels-in-Chief here in one room is unique. I do not think it has happened before. We are proud to be a part of this day."