The Duke and Duchess of Cambridge are attending a service to mark 100 years since the German invasion of Belgium at the start of World War One.
The Royals were received at L’Abbaye Saint-Laurent in Liege by King Philippe of Belgium, from where they will walk to the Cointe Inter-allied Memorial for a service which will include wreath laying and a minute’s silence.
Among the more than 50 heads of state joining them were French President Francois Hollande and German PresidentJoachim Gauck.
It is one of a series of events markingBritain’s entry into the Great War.
Across the Channel, the Prince of Wales, dressed in the uniform of a British admiral of the fleet, was attending a Service of Remembrance at Glasgow Cathedral where the 1,400 invited guests included representatives of Commonwealth countries, senior military figures, charities and cross-faith groups.
He will later lay a wreath at the Cenotaph in George Square.
At the other end of the UK his son, Prince Harry, will inspect a parade of troops in Folkestone – marking the route taken by millions of young men who marched through the Kent harbour town on their way to northern France and Belgium.
He will officially open a Memorial Arch in dedication to the veterans of the Great War, before joining William and Kate, and Mr Cameron, later this evening at a special ceremony at Belgium’s St Symphorien Cemetery, outside the town of Mons.
Speaking outside Glasgow Cathedral this morning, Prime Minister David Cameron said the war “profoundly changed our world”.
“It is right to commemorate this because this event had a massive impact on every community, every family on our country,” he said.
“It helped shape our world. The scale of the slaughter was immense.
“It is also right to remember the outbreak of the war because so many young British people thought they were rallying to a cause of defending the right of a small country, Belgium, to exist, and the prevention of the domination of Europe by one power.
“There are principles and thoughts that were in play at that time and are worth remembering today as well,” he added.
Across the globe, Australia and New Zealand also marked the ourbreak of the Great War withPrime Ministers Tony Abbott and John Key describing it as a conflict that shaped their nations too.
People are being urged to turn off their lights for an hour at 10pmto mark the moment the UK entered the war, 100 years ago.