Heads Together released a short film showing William discussing mental health issues with the US popstar Lady Gaga, who has gone public with her own struggles with post-traumatic stress disorder (PTSD) after she was raped aged 19.
In their video call - released on the Royal Family's Facebook page - they discussed ending the stigma.
She died when Prince William was 15-years-old, and Harry, 12.
Speaking without notes, the Duke went on to say: "So many parts of what I go and visit and people I meet, mental health is at the key heart of all their problems, whether it's homelessness, veterans' welfare, addiction, many of that stems from mental health issues".
Harry revealed that he had sought counselling in his late 20s following two years of "total chaos" which led him close to "a complete breakdown on numerous occasions".
The Duke of Cambridge said the death of his mother, Diana, Princess of Wales, in a Paris vehicle crash when he was 15, spurred him on to tackle the issue of mental health.
"I still think it's an incredibly fearless and an admirable thing to do and I think it's going to make such a difference in the lives of many people to hear him be so open about it".
He added: "During those years I took up boxing, because everyone was saying boxing is good for you and it's a really good way of letting out aggression".
He says he wants people to treat mental health the same way as physical health because then everyone can feel comfortable talking about it and not feel ashamed.
It's not every day Lady Gaga makes a coffee and has a Skype chat with the Duke of Cambridge but today seems to be the day. "It's really important to have this conversation and that you won't be judged".
Harry was 12 years old when she was killed in a auto crash but he said it was not until his late 20s that he processed the grief. There's a lot of shame attached to mental illness.
Prince William and Harry's magazine interview coincided with the release of Prince Harry's personal account of how he struggled to cope with his mothers death in a podcast with Bryony Gordon from the Telegraph.