He "shut down all his emotions" for almost two decades after losing his mother, Diana, Princess of Wales, despite his older brother, Prince William, trying to persuade him to seek help, the 32-year-old said in an interview published by the Telegraph today.
Disclosing that he has spoken to a professional about his mental health, he describes how he only began to address his grief when he was 28 after feeling "on the verge of punching someone" and facing anxiety during royal engagements.
"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," Harry said.
"I have probably been very close to a complete breakdown on numerous occasions when all sorts of grief and all sorts of lies and misconceptions and everything are coming to you from every angle," he added.
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Describing the "quite serious effect" that losing his mother had on his personal and professional life, he tells how living in the public eye left him feeling he could be "very close to a complete breakdown on numerous occasions."
The Prince turned to counsellors and even took up boxing. He says he is now in "a good place".
Prince Harry has decided to give an unprecedented insight into his past in the hope it will encourage people to break the stigma surrounding mental health issues.
Diana and her boyfriend Dodi Fayed were killed in a tragic car crash in a Paris underpass on August 31, 1997, along with their French driver Henri Paul as they tried to outrun chasing photographers.
Her death triggered a mass outpouring of public grief and Harry walked behind her coffin during a funeral which was broadcast around the world.
Harry said he recently confronted the grief of losing his mother as well as tackling the pressures of a royal life including overcoming a feeling of "fight or flight" during engagements.