Prince Harry has revealed he sought counselling after two years of "total chaos" having spent 20 years "not thinking" about his mother's death.
When his mother Diana, Princess of Wales, was killed in a car crash Harry was 12-years-old but he said it was not until his late 20s that he processed the grief.
The 32-year-old told the Daily Telegraph: "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."
He then started to have a few conversations about it and "all of a sudden" all the grief he had "never processed" before started to come to the forefront.
The prince sought help after his brother, Prince William, told him: "Look, you really need to deal with this. It is not normal to think that nothing has affected you."
Harry said boxing "saved" him when he took it up to deal with his aggression. He told the paper he came close to punching someone when he was 28.
He said: "It was 20 years of not thinking about it and two years of total chaos."
The prince said counselling had been "great" but he was now in a "good place" because of the "process I have been through over the past two and a half years".
He added: "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."
Harry is spearheading the Heads Together mental health campaign alongside his brother and sister-in-law, the Duchess of Cambridge.
The organisation is the London Marathon's charity of the year, and the three are hoping to make the race the "mental health marathon".
Bryony Gordon, who interviewed the prince for the paper and who has previously spoken of her struggles with bulimia and obsessive compulsive disorder, is running the 26.2 mile course for the campaign.
Harry, William and the Duchess of Cambridge will hand out medals at the race finish line on The Mall on Sunday.