Prince William has said the death of his mother 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.
The Duke of Cambridge's words come a day after his brother, Prince Harry, opened up about his own mental health struggles following the death of Diana, Princess of Wales.
This summer is the 20th anniversary of Diana's death in a car crash in Paris.
She died when Prince William was 15-years-old, and Harry, 12.
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.
Staying silent about mental health issues is "killing people", the 34-year-old cautioned.
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.
"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...
"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."
The second-in-line to the throne praised the runners who took part in the documentary, saying they had dealt with "issues that none of [them] should ever have had to face".
The three young royals 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.
The 10 runners are running for Heads Together, 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.