King Charles reportedly ordered his sons to set aside their ongoing feud ahead of Queen Elizabeth's funeral, leading them to reunite in public for the first time in over a year.
Royal sources said Prince William extended an "eleventh-hour olive branch" to his younger brother Prince Harry by offering him to join on the walkabout outside Windsor Castle following a phone call with his father Charles, the Daily Mail reported.
Hundreds of people gathered at the gates of Windsor estate on Saturday afternoon (local time) to mourn the Queen's death, and Princes William and Harry walked side-by-side with wives Kate and Meghan to greet the crowd.
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.
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 Sussexes, who are based in California, were in the United Kingdom on a pseudo-royal tour when the Queen's health deteriorated on Thursday.
It's believed they hadn't made any plans to meet with the Waleses, the Daily Mail reported, even though they were staying in Frogmore Cottage, which is about 600 metres from William and Kate's Adelaide Cottage. The brothers had both travelled to Balmoral Castle on Thursday after it was clear the Queen's health was faltering.
While a Kensington Palace spokesperson said the Prince of Wales had invited the Sussexes to join him and the Princess of Wales during the walkabout, according to The Times, extended negotiations were needed before the four of them met with the public.
"The Prince of Wales invited the Duke and Duchess of Sussex to join him and the Princess of Wales earlier," a senior palace source said, according to the Daily Mail.
"The Prince of Wales thought it was an important show of unity for the Queen at an incredibly difficult time for the family."
But later, journalist Omid Scobie, who is a friend of the Sussexes and has written an unofficial biography about them, said the invite came at the eleventh hour.
"The Waleses had always been scheduled to greet well-wishers at Windsor Castle, but royal sources say the decision to invite the Sussexes was made in the eleventh hour. It is, without a doubt, a significant moment in the history of the relationship between the two brothers," Scobie tweeted.
"Just as we saw after the death of Prince Philip and at his funeral, these are the moments when members of the royal family can put differences to one side to focus on the loss that has brought them together. Today's public reunion was a show of the utmost respect to the Queen."
Saturday's surprise appearance is believed to be the first time the two couples have been in public together since Commonwealth Day on March 9, 2020. It is also the first time William and Harry had been seen publicly together since July 2021 when they opened a memorial in honour of their mother, Princess Diana.
During the walkabout at Windsor Castle, 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."