The new Prince of Wales was accompanied by his wife Catherine, Princess of Wales, while Harry was joined by his wife Meghan, Duchess of Sussex. It is the first time the royals have appeared together since their falling out, meeting members of the public outside the palace following the death of Queen Elizabeth on Thursday (September 08).
The two brothers and their wives spent some time looking at the flowers and other tokens of respect left by the public at the royal residence.
They then shook hands with those present and received bouquets of flowers from them.
The visit to Windsor Castle marks William and Harry's first public appearance together since the Queen's death.
A royal insider told PEOPLE that William viewed the walkabout as 'an important demonstration of unity at an incredibly difficult time for the family'. William had previously paid a heartfelt tribute to the Queen, who died aged 96. The prince - who has children Prince George, 9, Princess Charlotte, 7, and Prince Louis, 4, with the Princess of Wales - also admitted he was still trying to come to terms with the loss of his grandmother. He said in a statement: 'On Thursday the world lost an extraordinary leader whose commitment to the country, the empires and the Commonwealth was absolute. In the days to come, so much will be said of the importance of their historical reign. However, I lost a grandmother. And while I will mourn her loss, I am also incredibly grateful. I have benefited from the Queen's wisdom and reassurance in my fifth decade. My wife had her guidance and support for twenty years. My three children were able to spend the holidays with her and create memories that will last a lifetime.”