The Duke of Sussex was diagnosed with Attention Deficit Disorder by a trauma expert during an interview.
Hungarian-Canadian physician Dr Gabor Maté said he came to the conclusion after reading Harry’s explosive memoir Spare.
He told the Duke: "Reading the book I diagnose you with ADD, I see it as a normal response to normal stress, not a disease."
Harry joked after the diagnosis: "Thanks for the free session."
During interview, which was broadcast live online, Harry also admitted he’d used psychedelic drugs to relax and previously took cocaine for a "sense of belonging".
He insisted he could not be himself as a royal and always “felt different”.
Viewers paid £19.12 to watch the livestreamed “intimate” chat, which was hosted by Harry’s publisher Penguin Random House. They also received a free copy of Harry’s book Spare.
Harry also told Dr Maté how he realised he needed to escape after undergoing therapy.
Harry, 38, said: "I realised that I’d learned a new language and people that I was surrounded by once, they didn’t speak the language - and so I actually felt more pushed aside."
He claimed sharing his trauma in bestseller Spare was an "act of service". Of negative reaction, he said: "The more they criticise, the more I feel the need to share."
Dr Maté said Harry’s "rich life" had been "deprived of touch" from his father and grandmother, the late Queen.
Harry said elements of his childhood were incredibly painful and that he always felt slightly different to other royals.
He drew parallels with his mother Diana, who died in a road crash in 1997 after divorcing Charles.
Harry said: "I felt strange being in this container and I know that my mum felt the same. It makes sense to me. I felt as though my body was in there and my head was out and sometimes it was vice-versa."
Asked whether readers would see Spare as him "wallowing in selfpity", Harry replied: "I definitely don’t see myself as a victim."
Asked about how it felt to "break free" by quitting the UK, Harry replied: "It feels great. Once the book came out I felt incredibly free.
He told Holocaust survivor Dr Maté how he was diagnosed with post-traumatic stress after seeking counselling over Diana’s death.
Harry said: "When I started to really unpack 12-year-old Harry at the point of where my mother died, that did start to unravel all sorts of other moments.
"It was scary. I turned what I thought was supposed to be sadness to try to prove to her that I missed her, to realising that actually she just wanted me to be happy. And that was a huge weight off my chest."
Harry said he’d used psychedelic drug ayahuasca to "deal with the traumas and pains of the past".
He said: "It was the cleaning of the windshield, the removal of life’s filters... it brought a sense of relaxation, release, comfort, a lightness that I managed to hold on for a period of time. I started doing it recreationally and started to realise how good it was for me. It is one of the fundamental parts of my life that changed me and helped me deal with the traumas and pains of the past."
Of cocaine, he added: "That didn’t do anything for me. More a social thing. It gave me a sense of belonging for sure.
"Marijuana is different, that did actually really help me. Alcohol is certainly more of a social thing."
Harry also claimed a lot of people in the armed forces "didn’t necessarily agree or disagree" with the invasion of Afghanistan, where he served as a helicopter pilot. He said: "You were doing what you were trained to do."
