After a very busy month of royal events, Prince Philip has decided to follow medical advice and skip upcoming commemorations to mark the Battle of Jutland.
A statement from Buckingham Palace said: "Following doctor's advice, the Duke of Edinburgh has reluctantly decided not to attend the commemorations marking the Battle of Jutland tomorrow in Kirkwall and Hoy."
Officials say Princess Anne will represent the royal family at the event.
Prince Philip, 94, is understood to have no plans to cancel any other forthcoming engagements, and has not attended hospital.
Buckingham Palace has refused to say what the ailment is.
The Battle of Jutland - the biggest naval engagement of World War One - began on 31 May 1916 when the Royal Navy's Grand Fleet, based at Scapa Flow, Orkney, clashed with the German High Seas Fleet.
We wish Prince Philip a speedy recovery!