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Britain's Prince William (L), Duke of Cambridge, Princess Astrid of Belgium (C) and Irish Prime Minister Enda Kenny attend the Battle of Messines Ridge commemorations in Messines on June 7, 2017. The Battle of Messines took place June 7-14, 1917 and was an offensive conducted by the British Second Army, during the First World War. / AFP PHOTO / EMMANUEL DUNAND (Photo credit should read EMMANUEL DUNAND/AFP/Getty Images)

Britain's Prince William (L), Duke of Cambridge, Princess Astrid of Belgium (C) and Irish Prime Minister Enda Kenny attend the Battle of Messines Ridge commemorations in Messines on June 7, 2017.
 The Battle of Messines took place June 7-14, 1917 and was an offensive conducted by the British Second Army, during the First World War. / AFP PHOTO / EMMANUEL DUNAND        (Photo credit should read EMMANUEL DUNAND/AFP/Getty Images)

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Britain's Prince William (L), Duke of Cambridge, Princess Astrid of Belgium (C) and Irish Prime Minister Enda Kenny attend the Battle of Messines Ridge commemorations in Messines on June 7, 2017. The Battle of Messines took place June 7-14, 1917 and was an offensive conducted by the British Second Army, during the First World War. / AFP PHOTO / EMMANUEL DUNAND (Photo credit should read EMMANUEL DUNAND/AFP/Getty Images)

Britain's Prince William (L), Duke of Cambridge, Princess Astrid of Belgium (C) and Irish Prime Minister Enda Kenny  attend the Battle of Messines Ridge commemorations in Messines on June 7, 2017.
 The Battle of Messines took place June 7-14, 1917 and was an offensive conducted by the British Second Army, during the First World War. / AFP PHOTO / EMMANUEL DUNAND        (Photo credit should read EMMANUEL DUNAND/AFP/Getty Images)

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Britain's Prince William (L), Duke of Cambridge, Princess Astrid of Belgium (C) and Irish Prime Minister Enda Kenny attend the Battle of Messines Ridge commemorations in Messines on June 7, 2017. The Battle of Messines took place June 7-14, 1917 and was an offensive conducted by the British Second Army, during the First World War. / AFP PHOTO / EMMANUEL DUNAND (Photo credit should read EMMANUEL DUNAND/AFP/Getty Images)

Britain's Prince William (L), Duke of Cambridge, Princess Astrid of Belgium (C) and Irish Prime Minister Enda Kenny attend the Battle of Messines Ridge commemorations in Messines on June 7, 2017.
 The Battle of Messines took place June 7-14, 1917 and was an offensive conducted by the British Second Army, during the First World War. / AFP PHOTO / EMMANUEL DUNAND        (Photo credit should read EMMANUEL DUNAND/AFP/Getty Images)

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(LtoR) Britain's Prince William, Duke of Cambridge, Princess Astrid of Belgium and Irish Prime Minister Enda Kenny attend a wreath-laying ceremony during the Battle of Messines Ridge commemorations at the military cemetery in Wijtschate, Belgium, on June 7, 2017. The Battle of Messines took place June 7-14, 1917 and was an offensive conducted by the British Second Army, during the First World War. / AFP PHOTO / POOL / FRANCOIS LENOIR (Photo credit should read FRANCOIS LENOIR/AFP/Getty Images)

(LtoR) Britain's Prince William, Duke of Cambridge, Princess Astrid of Belgium and Irish Prime Minister Enda Kenny attend a wreath-laying ceremony during the Battle of Messines Ridge commemorations at the military cemetery in Wijtschate, Belgium, on June 7, 2017.

The Battle of Messines took place June 7-14, 1917 and was an offensive conducted by the British Second Army, during the First World War.

 / AFP PHOTO / POOL / FRANCOIS LENOIR        (Photo credit should read FRANCOIS LENOIR/AFP/Getty Images)

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(LtoR) Britain's Prince William, Duke of Cambridge, Princess Astrid of Belgium and Irish Prime Minister Enda Kenny look at tombstones as they arrive to attend a wreath-laying ceremony during the Battle of Messines Ridge commemorations at the military cemetery in Wijtschate, Belgium, on June 7, 2017. The Battle of Messines took place June 7-14, 1917 and was an offensive conducted by the British Second Army, during the First World War. / AFP PHOTO / POOL / FRANCOIS LENOIR (Photo credit should read FRANCOIS LENOIR/AFP/Getty Images)

(LtoR) Britain's Prince William, Duke of Cambridge, Princess Astrid of Belgium and Irish Prime Minister Enda Kenny look at tombstones as they arrive to attend a wreath-laying ceremony during the Battle of Messines Ridge commemorations at the military cemetery in Wijtschate, Belgium, on June 7, 2017.

The Battle of Messines took place June 7-14, 1917 and was an offensive conducted by the British Second Army, during the First World War.

 / AFP PHOTO / POOL / FRANCOIS LENOIR        (Photo credit should read FRANCOIS LENOIR/AFP/Getty Images)