LONDON — Prince William, who has long spoken publicly about his emotional struggles, has taken his campaign for mental health awareness to Davos, Switzerland, urging global leaders to help break the stigma.

Prince William, the Duke of Cambridge, who is second in line to the British throne, spoke candidly on Wednesday about the difficulty he faced in trying to get celebrities to sign on to his cause, revealing — without naming names — that not one had initially offered to join the mental health campaign that he has run since 2016 with his wife and his brother.

It was only once they went public with their Heads Together campaign and “people realized that Catherine, Harry and I put our necks on the line here,” he said, that well-known names began supporting the effort. Its advocates now include the actress Judi Dench.

At the World Economic Forum’s annual meeting in the Swiss mountain resort of Davos, Prince William interviewed David Attenborough, the film producer of nature programs and a respected voice on climate change, on Monday. But he also spoke of the silence about mental health that was common in his parents’ and grandparents’ generations, and he called for people to be more open about their emotions.