Prince Harry was just 12 years old when his mother was killed in a car accident.
In a remarkable interview, the Prince spoke frankly about his mental health for a full 30 minutes.
He said the death of his mother had "a quite serious effect" on his mental health, leading to grief and anxiety he didn't address until his late 20s.
He counted himself lucky that after 20 years of avoiding the grief, he had only two years of "total chaos".
"I can safely say that losing my mum at the age of 12 and therefore shutting down all of my emotions for the last 20 years has had a quite serious effect on my personal life, but also my work as well," he told Bryony Gordon for her podcast, Mad World.
Prince Harry said he only sought help three years ago, after his brother Prince William told him he needed to deal with his grief.
"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 I need to deal with.'"
'I've spent most of my life saying I'm fine'
After burying his head in the sand for "many, many years", he said he had spoken to a number of professionals about his mental health and taken up boxing, and was doing much better.
"Saying you're fine is so much easier than going into the details", Prince Harry told Ms Gordon.
But "if you stay silent, it's more likely to kill you", he warned.
"Once you start talking about [your mental health], you suddenly realise you're part of quite a big club.
"It's a real community, and everyone's gagging to talk about it," he said.
The effects of war
Prince Harry insisted his mental health problems were not related to his time spent serving in Afghanistan.
"I can safely say it's not Afghanistan-related. I'm not one of those guys that has had to see my best mate blown up next to me and have to apply a tourniquet to both their legs. Luckily, thank God, I wasn't one of those people."
But the prince said that for many, traumas from youth and issues like anxiety and alcoholism rose to the surface while serving.
Afghanistan was "the trigger for all of these issues to come forward", he said.
Princely advice: See a shrink
The Prince said keeping quiet about issues is going to make it worse for yourself and for everyone around you.
"Through a lot of my 20s, I was a problem. I didn't know how to deal with it."
But he said speaking to a shrink or a psychologist makes a huge difference - for everyone.
"Everyone has a stressful week Monday to Friday. Wouldn't it be great if everyone had someone to speak to where you could offload all of your week's grief… all of the day to day sh*t everyone has to put up with."
"I can safely say once I offload my stuff to somebody else, I feel so much better."
If you wish to talk to someone about mental illness, you can call Lifeline on 0800 543 354.