Prince Harry has been hailed for changing attitudes after revealing he sought counselling to come to terms with the death of his mother.
Harry , who was 12 years old when Diana, Princess of Wales, was killed in a car crash, said it was not until his late 20s that he processed his grief.
In an interview with the Daily Telegraph, the 32-year-old said he spent nearly 20 years "not thinking" about her death and eventually got help after two years of "total chaos".
The prince's decision to speak out was described as "a true turning point" by mental health charity Mind, while campaign group Time to Change said he "will have helped change attitudes" by sharing his experiences.
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It comes amid calls for mental health education to be made compulsory in schools.
An open letter to The Times, organised by Lauren Callaghan, co-founder of the Shaw Mind Foundation, said mental health should be valued alongside academic achievement in schools.
The letter, signed by more than a dozen clinical psychologists and psychiatrists, states: "Schooling focuses on physical and academic education but neglects mental wellbeing.
"By educating young people about mental health and wellbeing in school, we can increase resilience and coping skills, boost awareness of mental health issues and encourage open, honest discussions about mental health."
Prince Harry, who is spearheading the Heads Together mental health campaign alongside the Duke and Duchess of Cambridge, admitted that shutting down his emotions after losing his mother had "a quite serious effect on not only my personal life but my work as well".
He told the Daily Telegraph: "My way of dealing with it was sticking my head in the sand, refusing to ever think about my mum, because why would that help?
"(I thought) it's only going to make you sad, it's not going to bring her back. So from an emotional side, I was like 'right, don't ever let your emotions be part of anything'.
"So I was a typical 20, 25, 28-year-old running around going 'life is great', or 'life is fine' and that was exactly it.
"And then (I) started to have a few conversations and actually all of a sudden, all of this grief that I have never processed started to come to the forefront and I was like, there is actually a lot of stuff here that I need to deal with."
The prince said he eventually sought help after his brother told him he needed to deal with his feelings. He told how boxing "saved" him by helping him deal with aggression after he came close to "punching someone" when he was 28.
"It was 20 years of not thinking about it and two years of total chaos," he explained.
Asked whether he had ever been to see a "shrink", he replied: "I've done that a couple of times, more than a couple of times, but it's great."
But the prince said that he was now in a "good place" because of the "process I have been through over the past two and a half years".
"I've now been able to take my work seriously, been able to take my private life seriously as well, and been able to put blood, sweat and tears into the things that really make a difference and things that I think will make a difference to everybody else," he said.
Paul Farmer, chief executive of mental health charity Mind, said : "It's inspiring to see Prince Harry speaking out about his experiences. It shows how far we have come in changing public attitudes to mental health that someone so high-profile can open up about something so difficult and personal.
"We know that this will have a huge impact on people who are still struggling in silence with their mental health - every time someone in the public eye speaks up we know that it encourages ordinary members of the public to do the same.
"Prince Harry speaking so candidly is a true turning point that shows that as a society we must no longer adopt a 'stiff upper lip' attitude and that we need to talk openly about mental health, something that affects us all directly."
Sue Baker, director of Time to Change, said: "Prince Harry sharing his experiences of mental health issues and the counselling he sought as a result of losing his mother will have helped change attitudes, not just at home but also overseas.
"It was a dream of mine 20 years ago that we'd see the royal family join sports people, music stars, politicians and business leaders as well as everyday people in sharing their mental health experiences in all sorts of communities."
Heads Together, an umbrella organisation for mental health charities, is the London Marathon's charity of the year.
The Duke and Duchess of Cambridge and Harry, who hope the race will be known as "the mental health marathon", will hand out medals on the finish line at the Mall on Sunday.
Harry will also open the London Marathon expo at the ExCel Centre in east London on Wednesday, where 39,000 runners will register ahead of the event.
Bryony Gordon, who interviewed the prince for the Daily Telegraph, has previously spoken of her struggles with bulimia and obsessive compulsive disorder and is running the 26.2-mile course for the campaign.