Queen Elizabeth II dies — follow the latest news as the world mourns
The king is not expected to attend any public events on Thursday and has returned to his Highgrove home in Gloucestershire.
The period will allow the king to pause, but it is understood he will be working to prepare for his new role and will already be receiving his red boxes of state papers.
The new monarch led the royal family in a public display of homage to the late queen on Wednesday by walking behind her coffin with his siblings, sons and other relatives as it was carried into Westminster Hall, where it will lie in state until the funeral on Monday.
Watched by tens of thousands lining the route from Buckingham Palace, the king delivered his mother to the hands of the nation for a period of four days.
The public pay their respects to Queen Elizabeth II at Westminster — in pictures
Every day of the year, except Christmas Day, he will receive from government ministers — and from representatives in Commonwealth and foreign countries — information in the form of policy papers, Cabinet documents and Foreign Office telegrams.
The correspondence also includes a daily summary of events in Parliament, letters and other state papers which are sent by his private secretary in the red boxes also used by government ministers to carry confidential documents.
Queen Elizabeth II's coffin procession from Buckingham Palace — in pictures
All of the papers have to be read and, where necessary, approved and signed.
The red boxes are made by leather goods company Barrow and Gale but it is not known if King Charles has received a new set or is using the queen’s boxes for the time being.
The late queen still used the boxes that were made for her on her coronation in 1953, having had them refurbished over the years.