The Queen was deeply hurt by public criticism of the way she handled Diana's death but agreed to address the nation as part of her sense of duty.
According to former senior courtier, Sir Malcolm Ross, who was in charge of organising the funeral, the monarch felt her priority lay with her grandsons in Scotland and both she and her staff were upset at the upsurge of feeling against them.
Despite this, he said, it was the sovereign who made the decision that her former daughter-in-law be honoured with a royal funeral.
And she also agreed to lower the Union flag at Buckingham Palace even though that went contrary to centuries old traditions.
Sir Malcolm said: "I knew the Queen would be very strong in her views. She didn't lower the standard on the death of her father and she wouldn't lower the standard on the death of anybody else. These protocols are crucial to maintain standards."
Even Diana's own sister, Lady Sarah McCorquodale, says she backed the monarch's judgement.
"If you were the grandmother of a 12-year-old and a 15-year-old whose mother had just been killed in a car crash, she did absolutely the right thing.
"If I had been her, I would have done that. Why would you bring them to London?
"Why don't you let them get over the start of the shock in the bosom of their own family?" she asks.
Former Prime Minister, Tony Blair, tells the BBC One documentary that it was "very difficult to work out exactly what the Queen was thinking at this time."
He said: "I think she was resistant to anything that struck her as false or struck her as a public relations event in the face of something that was a profound personal tragedy.
"Princess Diana's relationship that she had with the monarchy and the relationship with Prince Charles, there was going to be a risk that the country' s sense of loss turned to a sense of anger and grievance and then turned against the monarchy. So the first conversation with the Queen was an important conversation.
"She was obviously very sad about Diana. She was concerned about the monarchy itself because the Queen has a very strong instinct about public opinion and how it plays."
His former aide, Anji Hunter, who played an intimate part in the arrangements for the funeral, said it was hugely painful for both the Queen and her husband to experience such public anger against them.
"It was very painful for him [Philip] and for the Queen to hear that their public that they had served so well through all these years were also beginning to turn against them."
Alastair Campbell, Mr Blair's spokesman, added that although the Queen and her husband were "hurt and aggrieved", they acknowledged that they would have to do something to publicly demonstrate their grief.
The documentary, Diana, 7 Days, marks the third occasion one or both of the princes have appeared on a television special talking about their mother's death.