The Prince said he spent almost two decades “not thinking” about his mother’s death and he “shut down all his emotions”.
The 32-year-old has disclosed he endured two years of “total chaos” resulting in him seeking help from a professional and that boxing provided him with a positive method of “letting out aggression”.
“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,” he told the Telegraph.
“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.”
The Prince has decided to speak out about his difficulties to encourage people to break the stigma that surrounds mental health issues.
“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?
“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,” he added.
Prince Harry said he finally acted when his brother, Prince William, pushed him to address the issue.
He said he has met with a professional “more than a couple of times” and described the experience as being “great”.
“Some of the best people or easiest people to speak to is a shrink or whoever – the Americans call them shrinks – someone you have never met before.
“You sit down on the sofa and say ‘listen, I don't actually need your advice. Can you just listen’. And you just let it all rip.”
Alongside his brother and his sister-in-law, Kate Middleton, Prince Harry is promoting the Heads Together mental health campaign, the London Marathon’s charity of the year.
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