Philippe Huguen, AFP | Britain's Prince Harry, Britain's Prince William, Duke of Cambridge and Canadian Prime Minister Justin Trudeau, walk at the Canadian National Vimy Memorial in Vimy, near Arras, northern France, on April 9, 2017.

On Sunday, near Arras in Northern France, a WWI battle centenary commemoration looked for all the world like a celebration – even a birthday party.

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Canadian pop stars entertained a massive crowd – organisers expected 23,000 – with ballads sung from the iconic white marble memorial at Vimy Ridge, turned into a stage. Canadian actors performed excerpts of soldiers’ letters. Dignitaries abounded. French President François Hollande spoke solemnly of Franco-Canadian friendship and this patch of land France gave Canada in gratitude in 1922. On stage, Britain’s Prince Charles quoted the Canadian nationalanthem, saying: “The Canadians at Vimy embodied ‘the true north, strong and free'.”

But it was Canadian Prime Minister Justin Trudeau and William, Duke of Cambridge, on hand with his brother Prince Harry, who earned unabashed whoops from a crowd that included 10,000 young Canadians on field-trip pilgrimages to make this page of their high-school history books come alive.

We are forever grateful for their sacrifice. #Vimy100 pic.twitter.com/QHEAjVC0Az — Justin Trudeau (@JustinTrudeau) April 9, 2017

On April 9, 1917, under the cover of a deafening barrage of artillery, thousands of young men surged out of the obscurity of the trenches at 5:30am and into the battle of their lives. It marked the first time all four Canadian divisions, made up of volunteers from all over Canada, would fight together for a