Prince Harry has said his mother would be "overwhelmed" by the sudden willingness to talk about mental health in the UK, claiming he was "just doing my bit" by speaking of his own counselling.
The 32-year-old it was part of his "duty and service" to the nation to share his own story, after persuading others to discuss their mental health, reported the Daily Telegraph.
His mother, he said, would have been "overwhelmed and hugely encouraged" by the mental health conversation now happening in the UK.
Prince Harry spoke as he visited the London Marathon Expo, to officially open the event and meet charity runners for Heads Together.
Earlier this week, he told the Telegraph he had sought counselling after experiencing "two years of total chaos" as he refused to speak about his mother's death.
Asked whether his mother, Diana, Princess of Wales, would be proud of the Heads Together campaign, he said: "I hope so. I think she would be proud of the campaign, proud of everybody involved, proud of us.
"But specifically proud of the UK for having this conversation.
"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."
After handing out registration packs to runners which included their official number, timing chip 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."
Prince Harry was asked whether he was in a good place as a result of dating US actress Meghan Markle, replying: "The point that we've learnt over this campaign is that if you're able and comfortable enough to be able to talk about certain issues, certain experiences, then you come out of it a far better person."
When questioned about his interview, it was suggested the Queen, his grandmother, would not have opened up in a similar way.
Prince Harry replied: "It was the right time to have that conversation and the right way to have it."
He went on to say: "Every single person that we've met has come to us and shared - we've been asking everybody else to share.
"Now if there's any way that our experiences in the past can help with that and help other people come forward, and if our experiences and sharing those experiences can help reduce the stigma for the rest of the UK - then that's where the duty and service bit comes in."
The Duke and Duchess of Cambridge and Prince Harry will be at the London Marathon on Sunday but will not be running themselves due to security reasons.
Prince 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, which was 200, but is now 700."
Asked what could be done about the "politically sensitive" subject of a lack of mental health services, he replied: "Of course it's politically sensitive."
He added: "It's not our job to make those changes, our job specifically for this campaign is to remove the stigma, to allow the conversation to happen."