British, Belgian royals to mark WWI battle centenary

Britain's Prince Charles, Prince William and William's wife, Kate, are joining Belgian royals and relatives of soldiers who fought in the Battle of Passchendaele to mark 100 years since the deadly offensive began.

More than half a million Allied and German troops were killed or wounded in the World War I battle in western Belgium, also known as the Third Battle of Ypres.

The Allied offensive, fought by British and Commonwealth forces from July to November 1917 in battlefields that turned to liquid mud, ended up barely moving the front line against the Germans.

Britain's royals are scheduled to join Belgium's King Philippe and Queen Mathilde on Sunday for a ceremony at the Menin Gate in Ypres, which is etched with the names of thousands of missing soldiers.