Charles and Camilla will also be in France.
[FONT="]Yes, official diary[/FONT][FONT="]:
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June 30
Her Majesty The Queen, The Duke of Edinburgh will attend a Service and Vigil on the Eve of the Centenary of the Battle of the Somme, in Westminster Abbey, London SW1.
The Duke of Cambridge, The Duchess of Cambridge, Prince Harry will attend a vigil at the Thiepval Memorial, Somme, France.
July 1
The Prince of Wales, accompanied by The Duchess of Cornwall, TRH The Duke and Duchess of Cambridge, Prince Harry and TRH The Duke and Duchess of Gloucester will attend the National Commemorative Event to mark the Centenary of the Battle of the Somme at the Commonwealth War Graves Commission Memorial to the Missing, Thiepval, France.
The Prince of Wales, accompanied by The Duchess of Cornwall and TRH The Duke and Duchess of Gloucester will attend the ceremony to mark the Centenary of the Battle of the Somme at the Ulster Memorial Tower, Thiepval, France.
The Prince of Wales, accompanied by The Duchess of Cornwall and TRH The Duke and Duchess of Gloucester will attend the Ceremony of Remembrance, hosted by the Government of Canada, to mark the Centenary of the Battle of the Somme at the Beaumont-Hamel Newfoundland Memorial, France.
The Prince of Wales and The Duchess of Cornwall, accompanied by The Duke and Duchess of Gloucester, will visit Carnoy Military Cemetery. The Duchess of Cornwall will lay flowers at the grave of her Great Uncle, Captain Harry Cubitt, who was killed during the Battle of the Somme while serving with the Coldstream Guards
The Princess Royal, Colonel-in-Chief, The Royal Newfoundland Regiment, will attend the National Ceremony of Remembrance for the Battle of Beaumont Hamel, at the National War Memorial, Water Street, St. John's, Newfoundland and Labrador, Canada.
The Princess Royal will lay a wreath at the Commonwealth War Graves, Mount Pleasant Cemetery, St. John's, Newfoundland and Labrador, Canada.
I’ve also noticed that the other royals, Duke of Kent, Countess of Wessex, etc., seem to have military engagements on this day also.