I spoke of my problems after Diana's death to smash stigma around mental health: Harry
Prince Harry says it was "only right" to speak about his problems coping with his mother's death because he wanted to encourage others to "smash that stigma" around talking about mental health.
The 32-year-old reflected on his decision to speak openly about the counselling he sought as he visited the London Marathon Expo to officially open the event and meet charity runners.
The Prince, who was just 12 when Diana, Princess of Wales, was killed in a car crash in Paris on August 31, 1997 said of his mother: "I think from her perspective she would be overwhelmed and hugely encouraged by the fact that the UK - not known for wanting to talk about mental health issues - has suddenly got to this point."
The London Marathon has made the Duke and Duchess of Cambridge and Harry's mental health campaign Heads Together its official charity, and, when he cut the ribbon to launch the Expo, five-year-old Mellisa Howse, whose father Tony Howse is running on Sunday, was on hand to help.
In an interview with the Daily Telegraph, Harry revealed he spent nearly 20 years "not thinking" about his mother's death and eventually got help after two years of "total chaos".
After handing out registration packs to runners, which included an official number and a Heads Together headband, he said: "I've shared, just as much as everybody else has during this campaign. And after how many years of listening to stories from veterans and their families and then specifically in this campaign, William, Catherine and I hearing some of the most heart-wrenching stories based around what people have experienced and then the mental anguish that's happened from then.
"It was only right to share my experiences to hope to encourage others to come forward and smash that stigma, to make it easier for them to talk about their own experiences - so I was just doing my bit. When you've heard so many stories from so many other people and if you can relate to that, then it's only right that you talk about your own experiences."
William, Kate and Harry's Heads Together initiative has been running for about a year and has been encouraging the public to come forward and speak about their mental health issues or be a sympathetic ear for someone in need.
They have been intensifying their campaign in the run-up to the London Marathon, and hoping the thousands of runners who will be pounding the streets of London on Sunday will be wearing their blue Heads Together headbands.
When questioned about his interview with the national newspaper it was suggested the Queen, his grandmother, would not have opened up in a similar way. Harry replied: "It was the right time to have that conversation and the right way to have it."
William, Kate and Harry will be at the London Marathon on Sunday but will not be running.
Harry said: "Yes, all three of us were tempted, but it was probably safer and easier for us not to, and to try and do our best to lead the campaign from the side and let the focus be on the Heads Together runners."