King vows to serve 'to the best of my ability' in Commonwealth Day video address
The King has pledged to continue to serve "to the best of my ability" in his first video message since his cancer diagnosis.
The message has been recorded to mark Commonwealth Day and will be played at the Commonwealth Day service at Westminster Abbey later.
Speaking in his role as head of the Commonwealth, the King stressed his determination to keep going despite his ill health, saying: "In recent weeks, I have been most deeply touched by your wonderfully kind and thoughtful good wishes for my health and, in return, can only continue to serve you, to the best of my ability, throughout the Commonwealth...
"My belief in our shared endeavours and in the potential of our people remains as sure and strong as it has ever been. I have no doubt that we will continue to support one another across the Commonwealth as, together, we continue this vital journey."
In a photograph, taken at the time of the recording in late February, the King is seen sitting in the White Drawing Room at Windsor Castle. His eyes appear a little bloodshot and there is redness around his mouth.
His cancer diagnosis and ongoing treatment would make a slight change in his appearance understandable. Palace sources continue to insist he is in good spirits and determined to carry out as much work as possible behind the scenes, while doctors urge him not to carry out public duties.
It means he won't be able to attend the Commonwealth Day Service in person. Last year was his first as monarch and head of the Commonwealth. Instead the Queen will step in for him this year, with the Prince of Wales also attending.
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They will be accompanied by the Duke and Duchess of Edinburgh, the Princess Royal, the Duke and Duchess of Gloucester and the Duke of Kent.
The annual celebration of the Commonwealth will draw on the theme of resilience, at a time when the Royal Family has faced increased scrutiny and speculation because of health troubles.
The King will stress in his address how unity was essential for the family of nations, saying: "I cannot say often enough that it is by coming together that we create the best chances to improve our world and the lives of people everywhere."
Marking 75 years since the establishment of the Commonwealth, the King also appears to allude to historical matters that continue to cause protests, including calls for him to apologise for the horrors of slavery.
In his message he says, "we must work together to understand each other's perspectives, including the inequalities and injustices which still resonate to this day. We must find ways of healing, and to support each other to pursue solutions".
Among the 2,000 guests will be Commonwealth secretary-general Baroness Scotland, the president of Malta, foreign ministers, high commissioners, senior politicians and dignitaries from across the Commonwealth, faith leaders and schoolchildren and young people from throughout the UK.