King Charles III has shaken hands and spoken to wellwishers queuing for hours in central London to file past the coffin of his mother, Queen Elizabeth II, after thanking emergency workers who are helping to stage the late monarch's funeral.
To cheers of "hip, hip, hurrah" and shouts of "God save the King", Charles on Saturday walked alongside part of the queue waiting to see the Queen's lying-in-state, asking those lining up how long they had been there and whether they were warm enough.
Prince William also chatted to the crowds wanting to honour the Queen who died aged 96 on Thursday.
People are continuing to flock to central London, adding to the already hundreds of thousands who have filed past the coffin in a solemn stream, to pay their respects to Britain's longest-reigning monarch - a testimony to the affection in which she was held.
With preparations for the state funeral on Monday well under way, the king visited police headquarters to thank emergency services workers involved in the planning.
Charles was also due to greet leaders of the 14 countries where he is head of state such as Canada and Australia, and have lunch with the governors general - the people who represent the monarch in overseas realms - at Buckingham Palace.
By lunchtime, Britain's culture ministry said the waiting time to reach the historic Westminster Hall where Elizabeth's body lies in state, with her oak coffin on a purple-clad catafalque, draped in the Royal Standard and with the bejewelled Imperial State Crown on top, was up to 16 hours.
In the silent hall, some mourners wept, many were tearful while current soldiers and veterans saluted their former commander-in-chief. Others fell to their knees.
Canadian Prime Minister Justin Trudeau and Australian Prime Minister Anthony Albanese were among the dignitaries to pay their respects.
Earlier, the government had said it would pause entry to the queue if demand became too high, adding: "Please do not travel."
The death of the Queen at her summer estate in the Scottish highlands has sparked an outpouring of emotion across the country and 10 days of choreographed events.
Having laid at rest in the Scottish capital for 24 hours the coffin was flown south to London, where tens of thousands of people crowded onto a normally busy road in driving rain to observe the flag-draped casket being driven to Buckingham Palace.
On Friday night, Charles joined his three siblings - Princess Anne and Princes Andrew and Edward - in a silent vigil at the coffin while their eight children, including William and Harry, will form their own ceremonial guard later on Saturday.
The funeral, to be attended by nearly 100 presidents and heads of government including those from Australia, United States, France, Japan, Jamaica and Canada, is likely to be one of the biggest ceremonial events ever held in Britain.
Later on Saturday, the focus will switch to the younger royals and their vigil.
William and his brother Harry, who have grown apart in recent years after Harry moved to the US, will both stand guard at the coffin in military uniform.
Harry served two tours of duty with the British Army in Afghanistan but so far has appeared in processions in morning suits after he lost his honorary military titles when he stepped back from public royal duties.
The two brothers will be joined by their cousins - Peter Phillips and Zara Tindall, the children of Princess Anne, Princesses Beatrice and Eugenie, the children of Prince Andrew, and Louise and James, the children of Prince Edward.