Diana's death spurred me to tackle issue of mental health, says William
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.
Speaking after the preview screening of a BBC documentary about a group of London Marathon runners with psychological problems, he also said the more "influential and very important" people open up about their "issues and their battles" the better.
His words are likely to be seen as praise for his brother Prince Harry, who has received plaudits for disclosing he sought counselling to come to terms with his mother's death.
The 20th anniversary of Diana's death is this summer. William was 15 years old and Harry just 12 when she was killed in a car crash in Paris on August 31 1997.
The Duke, along with his wife Kate and Harry, has been campaigning through their mental health campaign 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 William 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, William said: "I really think this is a pivotal moment in the change of mental health.
"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.
"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."
William, Kate and Harry feature in the documentary, which charts the progress of 10 runners who take on the challenge of this year's London Marathon to aid their recovery from various mental health issues.
They are running for the royal trio's Heads Together mental health campaign which is the charity of year for the global sporting event taking place on Sunday.
Before the preview screening of the documentary - which will be aired on Thursday - the Duke met the runners and posed for a picture with the group during a reception hosted by the BBC's director of content, Charlotte Moore.
He chatted to Jake Tyler, 31, from Brighton, who is halfway through a 3,000-mile (4,828km) walk around Great Britain to raise awareness about mental health and help his depression.
Mr Tyler said: "It's not so much about us, it's trying to get the message out there, there's no harm in talking about (mental health). It can be really empowering and can lead to the achievement of amazing things. We'll all cross the finishing line at the London Marathon - a year ago I was in the worst place personally I've ever been - it will be great for people to see that."
Speaking about his issues, he added: "I was running a bar in Shoreditch and I think years of mismanaged stress and self-medicating and not taking very good care of myself - I've always lived with depression - I just wasn't doing myself any favours and I became suicidal while I was working; that was the first time I felt I needed help."
In the video featuring the Duke and global superstar Lady Gaga, the pair chatted about the importance of speaking about mental health issues, with the singer saying that talking more openly about problems would allow those dealing with them to feel like "we are not hiding any more".
Talking about her decision to speak out, she added: "Even though it was hard, the best thing that could come out of my mental illness was to share it with other people and let our generation, as well as other generations, know that if you are feeling not well in your mind that you're not alone and that people that you think would never have a problem, do.
"We have to make the strongest, most relentless attempt we can to normalise mental health issues, so that people feel like they can come forward."
Speaking from Kensington Palace to Lady Gaga at her home in Hollywood, William told the singer: "It's OK to have this conversation, it's really important to have this conversation and that you won't be judged.
"It's so important to break open that fear and that taboo which is only going to lead to more problems down the line."
The pair also made plans to meet when Lady Gaga comes to the UK in October, and the singer said: "We have to make the strongest, most relentless attempt we can to normalise mental health issues so that people feel like they can come forward."
Both William and Harry have been increasingly vocal about the importance of openness around mental health.
The Duke has highlighted the importance of role models speaking about their feelings, applauding grime artist Stormzy for talking about suffering from depression, and has said he and Kate want Prince George and Princess Charlotte to feel comfortable about discussing their emotions.
He told charity publication CALMzine: "Over the past year we have visited a number of schools together where we have been amazed listening to children talk about some quite difficult subjects in a clear and emotionally articulate way, something most adults would struggle with.
"Seeing this has really given me hope things are changing and there is a generation coming up who find it normal to talk openly about emotions."
William praised Stormzy's revelation about his depression as "incredibly powerful", saying: "There may be a time and a place for the 'stiff upper lip', but not at the expense of your health."
In an interview with the Daily Telegraph, Harry, 32, said he spent nearly 20 years "not thinking" about her death and eventually got help after two years of "total chaos".
He admitted shutting down his emotions after losing his mother had "a quite serious effect on not only my personal life but my work as well", and that he eventually sought help after his brother told him he needed to deal with his feelings.
Responding to his comments, Prime Minister Theresa May said: "Mental health problems affect people of all ages and all backgrounds.
"The bravery of those in public positions who speak out about their experiences helps smash the stigma around mental health and will help thousands of people to realise they are not alone."