It is a speech he has been preparing to deliver his whole life.
The new King, Charles III, will address the nation following the death on Thursday of his mother, Queen Elizabeth II.
A detailed list of royal protocol has been actioned following the Queen's passing in Balmoral, and this includes the new monarch delivering a televised address to the country.
When is King Charles's speech?
The King will make a televised address to the nation on Friday, which will be broadcast at 6pm.
The speech will be prerecorded.
Watch: King Charles pays tribute to his mother the Queen
In his address, Charles is expected to pay tribute to the Queen and pledge his duty to his service as the new monarch.
It is thought his speech will echo the famous words from his mother, in a radio broadcast from Cape Town, South Africa, on her 21st birthday on 21 April 1947.
She said: "I declare before you all that my whole life whether it be long or short shall be devoted to your service and the service of our great imperial family to which we all belong."
How can I watch King Charles's speech?
The speech will be broadcast on the BBC News channel and Sky News, as well as on BBC One and ITV and other major channels.
What has King Charles said already?
Charles became king immediately upon the death of the Queen on Thursday.
Following her passing, he said in a statement: "The death of my beloved mother, Her Majesty The Queen, is a moment of the greatest sadness for me and all members of my family.
"We mourn profoundly the passing of a cherished sovereign and a much-loved mother.
"I know her loss will be deeply felt throughout the country, the realms and the commonwealth, and by countless people around the world.
"During this period of mourning and change, my family and I will be comforted and sustained by our knowledge of the respect and deep affection in which the Queen was so widely held."
What else is happening on Friday?
The King and his wife, Camilla, now the Queen Consort, will travel from Balmoral to London.
At midday, church bells are expected to ring out across the country in commemoration of the Queen, and at the same time, prime minister Liz Truss will lead tributes at the House of Commons.
At 1pm, gun salutes, one round for every year of the Queen’s life, will be fired in London’s Hyde Park and at other stations.
King Charles will have his first audience as monarch with Truss this afternoon.
Charles is also likely to meet the Earl Marshal, the Duke of Norfolk, who is in charge of the accession and the Queen’s funeral, to approve the schedule for the coming days.
Watch: From Prince Charles to King Charles III