Diana died in a car crash in Paris in 1997, when Harry was 12 and his brother Prince William was 15.
Harry, now 31 and fifth in line to the throne, said he had not discussed his mother’s death until three years ago, the BBC reported.
“I really regret not talking about it,” he said. “For the first 28 years of my life, I never talked about it.”
He added, “It is OK to suffer, but as long as you talk about it. It is not a weakness. Weakness is having a problem and not recognising it and not solving that problem.”
Harry, who is the queen’s grandson, was speaking last week at a barbecue he hosted for the mental health charity Heads Together, attended by sports starts such as former England footballer Rio Ferdinand and Olympic athlete Kelly Holmes.
“I think the key message here is that everyone can suffer from mental health issues, whether you’re a member of the royal family, whether you’re a soldier, whether you’re a sports star,” said Harry, a former army officer who served in Afghanistan.