Prince Harry has admitted he had counselling after going off the rails in his 20s, years after the death of his mother.
He said he endured two years of "total chaos" almost 20 years after he "shut down" his emotions following the road accident that killed Princess Diana.
Speaking to the Daily Telegraph, he said he had only tackled his grief when he was 28 and faced with the feeling that he was "on the verge of punching someone".
As a result, he spoke to a "shrink... more than a couple of times".
He said he was inspired to speak out because of his involvement with mental health charity Heads Together.
The royal told the newspaper: "I sort of buried my head in the sand for many years.
"Losing my mum at the age of 12 and shutting down all of my emotions for the last 20 years has had a quite serious effect on, not only my personal life, but on my work as well.
"It was only three years ago... from the support around and my brother and other people saying 'you really need to deal with this - it's not normal to think that nothing has affected you'.
"My way of dealing with it was sticking your head in the sand - refusing to think about my mum because why would that help? I was like 'don't ever let your emotions be part of anything'.
"I was a typical 28-year-old going 'life is fine', and then I started to have a few conversations and then all of this grief that I never processed came to the forefront.
He continued: "It was only two years and I can count myself very lucky - two years of not thinking about it and two years of total chaos.
"I didn't know what was wrong with me. I thought it was part of growing up or whatever, but everyone said 'that makes total sense'."
The prince, fifth in line to the throne, said as a result of his conversations he was in "a good place now" and admitted he was able to take his work and private life "seriously".
He said he now believed, from his experience, that everyone's mental health would be better if there was the right person to "offload" all their problems on to.
Harry said he, his brother William and his sister-in-law Catherine felt that it was an important to raise mental health as an issue because they had all come across many people who were "struggling".
He said: "We thought the three of us have never come together on an issue. We all have different passions to the cause. We all have different reasons for doing it. Yes, fine, we have personal reasons. But it seemed like the right time."
He said he wasn't sure why people in the UK find it hard to talk about mental health, but it was possible it was British "stiff upper lip".
The prince said he had probably come close to a breakdown on numerous occasions as a result of grief, "lies, misconceptions and everything else that's coming at you", but he accepts that "it comes with the job".
For a period, he took up boxing because he "was on the verge of punching someone and punching someone with pads was easier".
The prince also offered advice to others who may be struggling: "Everyone has their stress. 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."