Prince William and Kate Join World War I Commemorations

— -- Britain's young royals -- the Duke and Duchess of Cambridge and Prince Harry -- represented their grandmother, Queen Elizabeth, while paying tribute to the fallen today at centennial events marking the outbreak of World War I and the more than 17 million people who died in the conflict.

Prince William and Kate, the Queen's granddaughter-in-law, joined King Philippe and Queen Mathilde of Belgium and world leaders, including French President Francois Hollande, for memorial ceremonies at the Allies Memorial at Cointe overlooking the Belgian city of Liege.

Kate, dressed in an Alexander McQueen cream coat dress and pleated skirt and pale floral hat, watched as William, adorned with the Queen’s Jubilee medals, addressed the gathered leaders and dignitaries.

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“The peace that we here enjoy together as allies and partners does not simply mean no more bloodshed –- it means something deeper than that," Prince William, 32, said. "The fact that the presidents of Germany and Austria are here today, and that other nations –- then enemies -– are here too, bears testimony to the power of reconciliation."

While observing that a war between the countries is now "unthinkable," Prince William pointed to the unrest in Ukraine in his remarks as an example of current tumult among countries.

"Not only is war between us unthinkable, but former adversaries have worked together for three generations to spread and entrench democracy, prosperity and the rule of law across Europe, and to promote our shared values around the world," William said.

"The events in Ukraine testify to the fact that instability continues to stalk our continent," he continued.

Prince William also thanked the Belgians for their sacrifice in 1914. Liege is in the eastern region of Belgium and took the brunt of Germany’s first attack. The Belgians' fierce resistance is a source of pride as it prevented the Germans from a quick victory.

King Philippe laid wreaths at the foot of the memorial, reminding those gathered of why the Belgian sacrifice was worthwhile.

“Peaceful Europe, unified Europe, democratic Europe. Peace is what our grandparents longed for," he said.

Prince Harry, wearing the ceremonial dress of the Blues and Royals, marked the World War I centenary with the unveiling of a Memorial Arch in Folkestone, where British troops marched to boats to fight on the Western Front.

The prince, himself a veteran who served in Afghanistan, laid a wreath at the town’s war memorial with a handwritten note that read, in part, “For all those who went down this road and never returned."

The centennial events taking place around Europe to mark the outbreak of World War I also included a memorial service at the Glasgow Cathedral attended by William and Harry's father, Charles, the Prince of Wales, and British Prime Minister David Cameron to honor the millions who lost their lives defending liberty.

"It is right to remember the extraordinary sacrifice of a generation and we are all indebted to them because their most enduring legacy is our liberty," Cameron said at the memorial.

Britain declared war on Germany at 11 p.m. on Aug. 4, 1914. Today, at the Tower of London, a river of 88,246 poppies are flowing out of the ancient moat, one poppy to represent each British life lost in WWI.

Continuing the tribute, Brits are being encouraged to turn off their lights tonight for one hour, starting at 10 p.m., and to leave one light burning as a symbol of hope. The Houses of Parliament, Big Ben, Tower Bridge, 10 Downing Street, St. Paul's Cathedral and other monuments across Britain will all go dark to commemorate the "hour of reflection."

In addition, a single candle will be lit at Westminster Abbey at 11 p.m. tonight to mark the precise moment Britain entered the war a century ago.

The Duke and Duchess of Cambridge and Prince Harry will return to the spotlight tonight to attend a twilight ceremony at St. Symphorien cemetery near Mons, Belgium. The Battle of Mons was the first major British action in World War I on the France-Germany and France-Belgium borders.

“We were enemies more than once in the last century, and today we are friends and allies," William said earlier today. "We salute those who died to give us our freedom. We will remember them."