The 32-year-old royal was just 12 years old when he lost his mother in 1997 after she was tragically killed in a car crash in Paris, France, at the age of 36, and has admitted he almost suffered a ''complete breakdown'' as he grew up determined not to think about the loss.
He said: ''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 not only my personal life but my work as well.
''I have probably been very close to a complete breakdown on numerous occasions when all sorts of grief and sort of lies and misconceptions and everything are coming to you from every angle.''
And the Prince - who is the younger brother of Prince William - admits he has been in therapy ''more than a couple of times'' in order to help him deal with his grief, and later turned to boxing as a way to vent his frustrations.
He added: ''During those years I took up boxing, because everyone was saying boxing is good for you and it's a really good way of letting out aggression. And that really saved me because I was on the verge of punching someone, so being able to punch someone who had pads was certainly easier.''
Prince Harry claims he refused to talk about his grief at first as he knew it wouldn't bring Princess Diana back, but admits after two years of ''total chaos'' he started to open up and felt better for doing so.
He said: ''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.''
And Harry also credits 34-year-old William with being a ''huge support''.
He said: ''It's all about timing. And for me personally, my brother, you know, bless him, he was a huge support to me. He kept saying this is not right, this is not normal, you need to talk to [someone] about stuff, it's OK.''
Harry is now campaigning to end the stigma surrounding mental health through his charity Heads Together - which he spearheads alongside William and Catherine, Duchess of Cambridge - as he hopes to ''make a difference to everybody else''.
Speaking to Bryony Gordon's 'Mad World' podcast for the Daily Telegraph newspaper, Prince Harry said: ''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.''
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