King Charles III said that he and his wife Camilla, the Queen Consort, had been "moved beyond measure" by everyone who paid respects.to his mother, the Queen, during the official ten-day period of mourning.
"As we prepare to say our last farewell, I wanted simply to take this opportunity to say thank you," he said in a statement issued by Buckingham Palace.
In the written message, the King said: "Over the last 10 days, my wife and I have been so deeply touched by the many messages of condolences and support we have received from this country and across the world.
"In London, Edinburgh, Hillsborough and Cardiff we were moved beyond measure by everyone who took the trouble to come and pay their respects to the lifelong service of my dear mother, the late Queen.
"As we all prepare to say our last farewell, I wanted simply to take this opportunity to say thank you to all those countless people who have been such a support and comfort to my family and myself in this time of grief."
On Sunday evening King Charles hosted a gathering for the heads of state attending the funeral with the country observing a minute's silence at 8.00 pm.
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After four days of the Queen lying in state, the doors of Westminster Hall were shut at 0.6.30 am on Monday.
Queues to file past the coffin were closed last evening at 10.40pm having earlier in the week reached an estimated waiting time of 22 hours.
The state funeral service at Westminster Abbey begins at 11:00am today.
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King Charles will walk behind the coffin when it is moved to Westminster Abbey alongside the Queen's other children, Princess Royal, the Duke of York and Earl of Wessex.
The Queen's grandsons, the Prince of Wales, the Duke of Sussex and Peter Phillips will walk behind them.
Following the service, a walking procession will see the coffin move from the Abbey to Wellington Arch at London's Hyde Park Corner.