World leaders and royals have gathered for ceremonies marking 100 years since Britain joined World War One.
Prince Charles and UK’s PM David Cameron attended a service in Glasgow, while Prince William and Kate Middleton are in Belgium with many heads of state.
At the Liege ceremony, Prince William paid tribute to the soldiers who “died to give us our freedom”.
The day concludes with a candle-lit vigil at Westminster Abbey and a “lights out” event around the UK.
The public can join the switch-off ending at 23:00 – the time Britain declared war on Germany in 1914.
About 17 million soldiers and civilians were killed between 1914 and 1918.
The day’s events began in Liege, Belgium, where 50 heads of state gathered for a service to mark the invasion of Belgium.
French President Francois Hollande said Belgium had been the first battleground of WWI and had offered “solid resistance” in Liege.
Speaking to the gathered European leaders, Prince William said: “We were enemies more than once in the last century and today we are friends and allies.
“We salute those who died to give us our freedom. We will remember them.”
Prince Harry unveiled a memorial arch in Folkestone, Kent – where a parade followed the route taken by millions of soldiers who marched to the harbor to begin their voyage to France in WWI.
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