A surprise moment unfolded when Prince Harry and his wife Meghan Markle joined Prince William and Princess Catherine in paying their respects outside Windsor Castle on Saturday afternoon (local time).
The two couples emerged from the same car, all wearing black, outside the castle and went on a 40-minute walkabout looking at a sea of floral tributes laid outside the gates of the royal estate in tribute to the late Queen Elizabeth II.
A large crowd greeted the Prince and Princess of Wales and the Duke and Duchess of Sussex with loud applause as they walked along the gates of Windsor Castle together.
The two couples greeted the crowd with William handed a Paddington Bear toy while Kate and Meghan were both given flowers by members of the crowd.
One well-wisher said it was "nice to see the family united in grief". "I think it's nice to see them all united here in town in which the Queen resided," the well-wisher said according to the UK's Telegraph.
"I'm sure she would have been absolutely delighted. As a nan myself, I'd be absolutely delighted if my grandchildren had made up and were reunited."
"It's a shame it's in grief but it's nice that they've come together.
A royal source described it as an important show of unity at an incredibly difficult time for the family. They emerged from the same car, all wearing black.
The two couples did not interact much during the 40 minute walkabout near one of the queen's favourite English homes, as they stopped to read messages left among the flowers, and shake hands and chat with the thousands of people lining the Long Walk.
At one point Meghan was hugged by a woman in the crowd while others stretched to shake hands and talk to the four royals in the early evening.
William spent some time bending down chatting to children, while Kate and Harry accepted flowers and messages of encouragement from those in the crowd.
Royal observers had been looking for signs of a detente amid the pomp and ceremony of a period of national mourning and Elizabeth's state funeral.
On Friday Charles used his first address to the nation as king to express his "love for Harry and Meghan as they continue to build their lives overseas".
He also bestowed on William and daughter-in-law Kate the titles of Prince and Princess of Wales, which he and his late wife Diana previously held.
William was heard telling one well-wisher that the days following the queen's death had been "so surreal".
"We all thought she was invincible," he said.
A Kensington Palace source said Prince William invited the Sussexes to join him and the Princess of Wales earlier on Saturday, according to the Daily Mail.
This was the first public appearance the royal couples have made together since the passing of the Queen on Thursday.
The Queen died aged 96 at her home in Balmoral, Buckingham Palace announced on Thursday.
"The Queen died peacefully at Balmoral this afternoon," the family said. "The King and The Queen Consort will remain at Balmoral this evening and will return to London tomorrow."
A royal source described it as an important show of unity at an incredibly difficult time for the family, according to Reuters.
The two sons of King Charles, use to be very close after the death of their mother Diana in a Paris car crash in 1997, but have fallen out in recent years after Harry and Meghan gave up their royal titles to move to the United States.
The joint outing has raised the prospect of a rapprochement between the brothers.
