Prince William has admitted speaking openly about his mother for a new documentary about her life was "daunting" at first but the process has been a "healing" one.
William described the 90-minute TV program as a "tribute" to Diana, that will remind the public - especially those too young to remember her - of the "warmth" and "humour" of his mother.
But the ITV documentary, to screen in the UK on Monday, will be the first and last time he, and Prince Harry, will speak candidly about their mother.
"We won't be doing this again - we won't speak as openly or publicly about her again, because we feel hopefully this film will provide the other side from close family friends you might not have heard before, from those who knew her best and from those who want to protect her memory, and want to remind people of the person that she was.
"The warmth, the humour and what she was like as a mother, which probably hasn't come across before in many other pieces and from other people."
William is interviewed extensively with Harry for the program, Diana, Our Mother: Her Life and Legacy, which also features the Princess' brother Earl Spencer and friends like Elton John.
Explaining his reasons for speaking candidly about Diana, William said: "Twenty years on Harry and I felt that it was an appropriate time to open up a bit more about our mother."
The 20th anniversary of her death will be marked with a statue of Diana erected in a place she knew well, the public gardens of her former home Kensington Palace.
"Harry and I feel very strongly that we want to celebrate her life and this is a tribute from her sons to her, and we want her legacy to live on in our work and we feel this is an appropriate way of doing that.
"To remind not only people who knew her, but also you have to remember this is 20 years ago now she died and there are people who don't even know about her.
"And I think it's been quite cathartic for us doing it. It's been at first quite daunting - opening up so much to camera...but going through this process has been quite a healing process as well."
