The Duke Of Cambridge attends a screening of the BBC’s ‘Mind Over Marathon’ Documentary The first part of the programme, Mind over Marathon, will be broadcast at 9pm on BBC One on Thursday. “I really think we’re on the cusp of something really big and I know the BBC are keen to continue covering mental health and really trying to make that change. “As you can see, you know, I have my own reasons for being involved in mental health – what happened to me with my mother when I was younger – but equally the charitable work I do at the moment and the areas that I’m involved in, it all comes back to mental health.”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. Diana, Princess of Wales, died on August 31, 1997, when Prince Harry was 12 and Prince William was 15. The Duke, along with his wife the Duchess of Cambridge and Prince Harry, has been campaigning for Heads Together to encourage the nation to speak about their psychological problems or to be a sympathetic ear.Lady Gaga has joined their campaign, teaming up with the Duke for a video, watched by thousands online, where they encouraged people to open up about their feelings and bring an end to the “shame” of talking about mental health issues. Speaking after the screening of the first instalment of the two-part Mind over Marathon documentary, at Old Broadcasting House, in central London, the Duke said: I’m speechless actually. I’m quite emotional. So I am just going to take a minute to calm myself down.”He went on to say: “I really think this is a pivotal moment in the change of mental health. The Duke of Cambridge poses with Mind over Marathon runnersCredit:Getty The Duke and Duchess of Cambridge and Prince Harry in their Heads Togther marathon bandsCredit:Getty “And we need to make mental health normal, we need to treat it the same way we treat physical health, it has to be seen in the same way.”And the more documentaries we have like this, the more we have influential and very important people speaking about their issues and their battles, the better.”In a separate video with Lady Gaga, the pop star, he said: “It’s time that everyone speaks up.” The Duke of Cambridge has said the death of his mother Diana, Princess of Wales, spurred him on to tackle the issue of mental health, as he pledges it is “time everyone speaks up”.Speaking after the preview screening of a BBC documentary about a group of London Marathon runners with psychological problems, the Duke said the more “influential and very important” people open up about their “issues and their battles” the better.His words follow widespread praise for his brother Prince Harry, who this week disclosed that he sought counselling to come to terms with his mother’s death. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.