Prince William, Prince Harry, Kate and Meghan greet mourners at Windsor Castle

They put aside their differences to view floral tributes to Queen Elizabeth II

Britain's William, Prince of Wales, second left, his wife Catherine, Princess of Wales, left, along with Prince Harry and his wife Meghan, the Duchess of Sussex, look at floral tributes as they walk outside Windsor Castle. Reuters

Left to right: The Duchess of Cambridge, Prince William, Prince Harry and the Duchess of Sussex at Windsor Castle. AFP

The royals meet people outside Windsor Castle. AP

Walking together outside Windsor Castle. Reuters

Prince Harry and his wife Meghan are staying at Frogmore Cottage on the Windsor estate, just a stone's throw from Prince William and his wife Kate's new home, Adelaide Cottage. PA

The royals speak and shake hands with different sides of the cheering crowds. AP

A pause to look at floral tributes laid by members of the public on the Long Walk at Windsor Castle. AFP

Prince Harry points at a floral tribute. Reuters

In his first speech as king on Friday, Charles, 73, spoke of his love for his second son and daughter-in-law. AP

The two couples had last been seen together at the Commonwealth Day service at Westminster Abbey in 2020. Reuters

Queen Elizabeth II dies — follow the latest news as the world mourns

Prince William and Prince Harry made a surprise joint appearance outside Windsor Castle with their wives, Kate, Princess of Wales and Meghan, Duchess of Sussex.

The brothers have reportedly fallen out in the years since Harry left front-line royal duties for a life in the US with his young family.

But on Saturday, all four put aside their differences to view floral tributes to Queen Elizabeth II that have been placed outside Windsor Castle, about 35 kilometres west of London.

They also met members of the public who were there to lay flowers and mourn the queen.

For William and Kate, the Windsor walkabout was their first public engagement since becoming Prince and Princess of Wales.

A royal source said the Prince of Wales had asked his brother and his wife to join them in viewing the tributes.

A well-wisher kisses the hand of King Charles III outside Buckingham Palace after the death on Thursday of Queen Elizabeth II. King Charles, who spent much of his 73 years preparing for the role, on Friday planned to meet the prime minister and address a nation grieving the only British monarch most of the world had known. He takes the throne in an era of uncertainty for his country and the monarchy itself. AP

King Charles III and Queen Consort Camilla arriving at Buckingham Palace, London, after travelling from Balmoral following the death of Queen Elizabeth II on Thursday. PA

King Charles and the queen consort outside Buckingham Palace. PA

King Charles and the queen consort view tributes left outside Buckingham Palace, London, after the death of Queen Elizabeth on Thursday. PA

King Charles greets well-wishers outside Buckingham Palace. AP

King Charles and the queen consort read messages left by mourners at Buckingham Palace in London. Queen Elizabeth II, Britain's longest-reigning monarch and a rock of stability through much of a turbulent century, died on Thursday, after 70 years on the throne. She was 96. AP

King Charles greets well-wishers at Buckingham Palace after the death on Thursday of his mother, Queen Elizabeth II. AP

King Charles and Queen Consort Camilla view tributes left outside Buckingham Palace after the death of Queen Elizabeth II. PA

Outside Buckingham Palace on the first day of public mourning after the death of Queen Elizabeth II. The queen's death at the age of 96 marks the start of a tumultuous 10 days for the UK in which a queen is buried, a nation will mourn its longest-reigning monarch, and a new king is proclaimed. Bloomberg

King Charles during a walkabout to view tributes left outside Buckingham Palace. PA

King Charles outside Buckingham Palace on Friday. AP

King Charles and Queen Consort Camilla surrounded by crowds of well-wishers in London. Reuters

The car carrying King Charles and the queen consort arrives at Buckingham Palace with the Union Flag at half mast. Getty Images

People gather at the Queen Victoria Memorial opposite Buckingham Palace on Thursday night after the death of Queen Elizabeth II. Reuters

People gather at the Queen Victoria Memorial opposite Buckingham Palace after the death of Queen Elizabeth II. PA

Mourners gather outside Buckingham Palace on Thursday night. PA

Tributes and candles left outside Buckingham Palace in London after the queen's death was announced. PA

Police officers stand among floral tributes left outside Buckingham Palace. PA

A member of the royal household staff posts a notice on the gates of Buckingham Palace announcing the death of Queen Elizabeth. AFP

Royal follower John Loughrey, wearing a Union Jack hat, photographs the official announcement of the queen's death. EPA

Mourners outside Buckingham Palace. Reuters

A man with a Union flag umbrella shelters from the rain near the Queen Victoria Memorial. AFP

Mourners on the Queen Victoria Memorial outside Buckingham Palace. PA

The crowds outside Buckingham Palace on Thursday night. PA

Mourners at the vigil outside Buckingham Palace. PA

Mourners at the vigil outside Buckingham Palace. PA

Londoners walk down The Mall that leads to Buckingham Palace on Thursday night. PA

Taxis lined up along The Mall leading to Buckingham Palace in London after the announcement of the death of Queen Elizabeth. PA

The advertising screens in Piccadilly Circus in London mark the death of the queen. Getty

An image of Queen Elizabeth II is displayed on The BT Tower in London. Getty

A bus stop on Tottenham Court road in London displays an image of the queen. Getty

Mourners gather outside Windsor Castle, Berkshire. PA

Flowers are left under the Queen Victoria statue outside Windsor Castle. PA

Candles and flowers form a makeshift memorial at the Queen Victoria statue outside Windsor Castle. PA

People lay floral tributes outside Balmoral Castle, Scotland, on Thursday night. EPA

People lay floral tributes outside Balmoral Castle, Scotland, Britain, 08 September 2022. EPA

People pay their respects at the gate of Sandringham House in Norfolk. PA

People pay their respects at the gate of Sandringham House in Norfolk. PA

The last time William was joined in public by his brother at Windsor Castle was at the funeral of the Duke of Edinburgh in April last year.

Both couples left in the same vehicle as Saturday's engagement, which lasted more than 40 minutes, came to a close.

All four were dressed in black as they walked along the gates of the castle.

At one point during the walkabout, Meghan was seen being given a close hug by a young girl in the crowd.

The duke and duchess held hands as they looked at the tributes, with Harry at one point affectionately putting his hand on Meghan's back.

Each member of the royal family was seen pointing at different tributes and discussing them as members of the crowd waved at them.

William and Kate and Harry and Meghan then greeted well-wishers at Windsor Castle, with a number holding up mobile phones to take a photo of the royals.

A crowd at the castle broke out into applause as the couples approached members of the public and spoke to them.

William was seen speaking intently to a member of the crowd, at one point shaking a woman's hand. Both William and Kate could be seen thanking people.

Kate crouched down at one moment and began speaking to a child who had started to cry.

The child stopped crying when Kate approached her.

Meghan was also seen shaking the hands of several children and well-wishers at Windsor.

She walked over to a section of the crowd and approached a teenager, who was seen putting her hand over her mouth in shock.

The duchess and her husband spoke briefly for a few moments and Meghan could be seen assuring a young girl by putting her hand on her shoulder.

The girl then said: “Can I have a hug?” and Meghan was seen nodding, before leaning in and giving her a big hug.

The touching moment was filmed by other members in the crowd.

The duke and duchess were handed bunches of flowers, which they both accepted.