Prince William has said that every celebrity he asked to back his Heads Together mental health initiative three years ago refused.
The Duke of Cambridge said “a lot” of people were approached, but no one wanted to be associated with mental illness.
Speaking at the World Economic Forum, in Davos, he urged firms to help people open up on the issue.
Heads Together was launched to help combat the stigma of mental health.
It was started in 2017 with the backing of the Duke and Duchess of Cambridge, and Prince Harry.
The duke also spoke about his own struggles with mental health, saying there was one traumatic incident that he didnâ€™t think he would “ever get over”.
He said if he hadnâ€™t opened up to colleagues about the situation, he would have “gone down a slippery slope” mentally.
Looking visibly emotional, he said he still found the incident “very difficult to talk about” because it was “related very closely to my children”, George, Charlotte and Louis.
The prince has spoken previously about “very traumatic” callouts involving children while working for the air ambulance.
But he said such feelings were “only human”, adding: “Yes, you put a suit of armour onâ€¦ but one day something comes along closely related to your own personal life and it really takes you over a line.”
Companies can do more
The issue of mental health is a big theme at this yearâ€™s Davos, with several sessions on the topic.
Studies show one in four people will suffer from mental illness at some point in their life, but many people are still too embarrassed to admit they have a problem.
Despite a greater willingness to discuss the issue, the prince said that a lot of stigma remains, meaning “so many people are suffering in silence”.
He added: “For some reason, people are embarrassed about their emotions - British people particularly,” he told a packed audience at Davos.
He feels the British stiff upper lip and stoicism in the face of uncertainty of previous generations has a lot to do with it. The attitude was passed onto children, especially during the First and Second world wars when it became difficult to talk about “such horrendous circumstances”.
But he said “a new generation knows thatâ€™s not normal” and is becoming aware that itâ€™s better to be open about how they are feeling.
The prince urged companies to do more. “It should be so much easier to go to HR and talk about it. It has to come from the top.”
Spotting the signs
During the debate, the audience was asked whether they or anyone they knew had suffered from a mental illness. Nearly everyone in the room raised a hand.
HSBC boss John Flint, talking on the same panel, said that in the “notoriously competitive” banking industry mental health problems were common.
He said it was imperative that people at the top spoke about it to allow those lower down in the organisation to open up.
“We all sit on the spectrum [of mental health]. I know thereâ€™s a profound difference between when Iâ€™m feeling my best and when Iâ€™m not,” he added.
Mr Flint said the bank was training managers to spot signs of mental health problems so they could help staff deal with them.
He said it made business sense given the impact problems had on workersâ€™ performance.