It was an action that meant the Royal Family was tearing up the protocol rulebook to support the nation in its unprecedented outpouring of grief.
Until yesterday only the Royal Standard, with its lions and fleurs-de- lys, had flown above the Palace roof to indicate that the Queen was in residence - and the standard has never been flown at half-mast because it symbolises the continuity of the monarchy.
The Queen ordered the break with tradition after mounting public anger that for most of last week Buckingham Palace's flagpole stood bare, in stark and seemingly uncaring contrast to central London's other flagpoles and to the mass of flowers at the palace gates, while the Royal Family remained at Balmoral.
A few minutes earlier, there was another sign that the deafening calls from the public for a more obviously humane approach to their mourning had told on the Royal Family, as the Queen led family members to the gates of the Palace, where they stood in silent tribute as Diana's coffin passed by.
As the cortege reached the gates of Buckingham Palace at 10.17am, the Queen stood on the pavement of Birdcage Walk with Princes Andrew and Edward, the Princess Royal, the Duchess of York, the Princesses Beatrice and Eugenie, Princess Margaret, the Duke and Duchess of Kent and Lord Linley.
They gathered at the gates facing Green Park, next to the mountains of flowers laid at the palace fence. And behind them was a banner, draped on the railings, that read "Diana, Princess of Love". The gesture was not lost on the crowd. Many who had been angry with the apparent aloofness of the royals earlier in the week said that they had been reassured by their actions.
Duncan Towse, 45, a sales engineer from Hove, East Sussex, said: "I think it is in keeping with everyone's wishes that they have responded in this way. I think protocol is important but when someone younger has died, it is good to show that they can be more flexible in their attitudes and be a little less emotionless.
"It will stand them in good stead for the future. Now, people can see that the Royal Family are more in tune with the values of today and the new millennium."
Fiona McGovern, 18, a customer care administrator from Wellingborough, Northamptonshire, said: "They needed to show that they were at least as upset as we are. We were grieving, but they had not done anything. But now they have, it has brought us together with the Royal Family again.
"Now we are aware of their grief as well as our own. I have always been a Royal Family lover, but this has made my feelings even stronger."
BJ Gray, 33, a PhD student from Loughton, Essex, said: "It's brilliant. It's exactly what they should have done - to go with emotion rather than protocol.
"It's the feelings of the people that matter, rather than what is written in stone. I think that it has given the message to the people that they do care about Diana and acknowledge her role in society."
A Buckingham Palace spokeswoman said the Queen had decided on Thursday to break with tradition over the flags. "This is a mark of respect for the Princess on the day of her funeral," she said. "It will fly at half- mast until midnight."Reuse content