The couples wave to members of the public at Windsor Castle, following the death of Queen Elizabeth. Photo / AP
The Prince of Wales and Duke of Sussex were reunited in sorrow alongside their wives on Sunday, setting aside their differences to meet well-wishers in Windsor and honour their grandmother Queen Elizabeth II.
The quartet came together to pay their respects to the late Queen, who Prince William said had been with them in their "happiest moments and saddest days".
The Prince had extended the hand of friendship to his younger brother, inviting the Duke and Duchess of Sussex to join him on a walkabout in Windsor to share their memories with the public.
It was the first public appearance for the new Prince and Princess of Wales since they were announced in the title by the King in his first address to the nation less than 24 hours earlier.
The four, who have rarely been seen together, stepped out on the Long Walk at Windsor Castle, in the first sign of a healing of the rift that has opened since the Sussexes left the working Royal family in January 2020.
A source said that the Prince of Wales believed the gesture was "an important show of unity at an incredibly difficult time for the family".
Moments earlier, the Prince had issued a statement in tribute to his "Grannie", whom he called an "extraordinary leader and Queen", who had offered his family "wisdom, reassurance, guidance and support".
The appearance by the Waleses and the Sussexes came at the end of a day in which the King was officially proclaimed monarch, in a ceremony at St James's Palace imbued with ancient ritual and broadcast on television for the first time.
The Queen Consort and the Prince of Wales had joined privy counsellors, including six former prime ministers, at the Accession Council.
His Majesty was proclaimed as King Charles III with the sound of trumpets, before spending the day holding audiences with the Prime Minister and Cabinet, opposition parties and the Dean of Westminster.
At the end of the day, the King left Buckingham Palace and got out of his car on The Mall to speak to well-wishers on Stable Yard.
Shouts of "God save the King" were heard along with a chorus of the national anthem. It was also announced that Queen Elizabeth II's state funeral would take place at Westminster Abbey, at NZST 10pm on Monday, September 19, which will be a bank holiday.
It is not yet known if there are plans for New Zealand to observe the day as a public holiday.
Buckingham Palace confirmed that the public would be invited to pay their respects over the course of nine days, with members of the Royal family to walk in processions and hold vigils to honour the late monarch.
The Queen's oak coffin has been lying in the Ballroom at Balmoral Castle and will be taken on a slow, six-hour journey by road to the Palace of Holyroodhouse in Edinburgh on Sunday.
From there, it will be taken to St Giles' Cathedral, in the Scottish capital, where it will remain until Tuesday before being flown to London.
The Queen's body will lie in state for four days at Westminster Hall from Wednesday, allowing for a continuous stream of members of the public who wish to pay their respects.
From Sunday, the King will begin his journey to the home nations to receive condolences, attending services of reflection in Scotland, Northern Ireland and Wales, and delivering speeches at each.
The Government is expecting "extremely large crowds in central London" during the period of mourning, with one of the largest crowd control operations in British history so that "as many people as possible are able to pay their respects". The King will lead mourning, with the Queen Consort by his side throughout.
Members of the Royal family will walk behind the coffin and hold vigils, but Buckingham Palace has not yet confirmed who will attend each event.
The Prince of Wales, speaking as a grieving grandson, encapsulated what Queen Elizabeth had meant to his own generation.
"The world lost an extraordinary leader, whose commitment to the country, the Realms and the Commonwealth was absolute," he said. "So much will be said in the days ahead about the meaning of her historic reign.
"I, however, have lost a grandmother. And while I will grieve her loss, I also feel incredibly grateful."
Shortly after issuing the written tribute, the Prince and Princess appeared outside Windsor Castle, joined by the Duke and Duchess of Sussex.
The couples have had a strained relationship, with a rift between the brothers that many feared would never heal after a series of allegations about the Royal family by the Sussexes.
The Prince is understood to have extended the invitation to the Sussexes to join him shortly before the walkabout, surprising thousands of well-wishers who had turned out to lay flowers in memory of the Queen.
The quartet, all wearing mourning clothes, spent about 45 minutes greeting people of all ages, accepting bouquets to lay on the growing pile of tributes and thanking the public for their kindness.
After chatting, hugging and sharing sympathies with members of the public for over 40 minutes, the Prince and Princess of Wales and the Duke and Duchess of Sussex have headed back into the Windsor Estate together. Both couples left in the same car, driven by William. pic.twitter.com/V2ettkmKnt
Queen Elizabeth II said the Sussexes remained "much-loved members of the family" after they left the working Royal family. The Duke and Duchess are now considering how to bring their children to the UK.