Twitter users reacted to Prince Harry's disclosure.
But "if you stay silent, it's more likely to kill you", he warned.
Instead of the usual PR warnings ahead of a big interview - "Don't ask about Diana" - Harry appears bursting to finally share the feelings of emotional isolation that gnawed away at him for two decades after his mother's death.
At royal engagements, Harry found himself overcome by a "flight or fight" sensation.
At the age of 28, and "on the verge of punching someone", the Prince eventually sought help. But he didn't understand what was causing the eruptions.
After going through all the stages of grief, including anger and aggression, during his "two years of chaos", Prince Harry turned to those closest to him for help.
"I've spent most of my life saying "I'm fine" ... and most of us aren't up for going that deep".
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.
It comes amid calls for mental health education to be made compulsory in schools.
Prince Harry with his mother. "There are ways and means to get round that stress and to cope with life in general and not only is that going to make it better for you but it's going to make it better for everyone else who cares for you and worries for you". In an article about the experience, she wrote, "Was this really happening?. I mean really really?"
Next Sunday, Heads Together will be the principle charity of the London Marathon.
Gordon was pleasantly surprised with the prince's honesty.
Harry along with Prince William and sister-in-law, Kate, have established Heads Together, a charity which promotes good mental health and open discussion about it.
The three have actively worked to alleviate mental health stigma.
Often, starting the conversation is the most hard hurdle in tackling mental health.
The 32-year-old prince tells the Telegraph that it took two years of "total chaos" in his late 20s before he realized that he needed to seek counselling.
Harry, 32, said he lived in chaos for about two years because of the 1997 auto crash that took his mother from him when he was only 12 years old, The Daily Telegraph reported. "I thought it was part of growing up or whatever, but everyone said "that makes total sense".
He later had a successful career in the British Army before leaving in July 2015.
"I can count myself very lucky", he said.
The Prince went on to explain that losing mom Princess Diana in 1997 on the "public platform" affected his personal and public life. He didn't let his "emotions be part of anything, he said, and tried to behave like a "typical" 20-something".
"Luckily, thank God." Grief that he'd never processed started to come to the forefront, he said, and he also dealt with a fight-or-flight reaction he had in certain public situations.
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