LONDON, ENGLAND - APRIL 18: Prince William, Duke of Cambridge speaks on stage at the screening of the BBC documentary 'Mind over Marathon' at BBC Radio Theatre on April 18, 2017 in London, England. The screening also launches the BBC season on mental health. (Photo by Chris Jackson - WPA Pool/Getty Images)

LONDON, ENGLAND - APRIL 18:  Prince William, Duke of Cambridge speaks on stage at the screening of the BBC documentary 'Mind over Marathon' at BBC Radio Theatre on April 18, 2017 in London, England.  The screening also launches the BBC season on mental health. (Photo by Chris Jackson - WPA Pool/Getty Images)