The Duke and Duchess of Cambridge and Prince Harry will join runners taking part in the London Marathon for their mental health campaign Heads Together.
Around 150 competitors who are running for the umbrella organisation will be joined by the royal trio on the London Marathon Community Track at the Queen Elizabeth Olympic Park in east London on Sunday for a training session.
William will give the runners words of encouragement and, with his wife and brother, set out how the marathon's 38,000 participants can make the 2017 Virgin Money London Marathon the "mental health marathon".
The three are expected to join the runners - who are fundraising for the eight Heads Together charity partners or the campaign itself - as they train and warm down.
Marathon world record holder Paula Radcliffe will give advice to the runners while British 400m record holder and London Marathon regular Iwan Thomas will join the training day and a question and answer session.
Heads Together, spearheaded by the three royals, aims to change the national conversation on mental well-being to a positive one, and is a partnership between eight charities that provide front-line mental health support.
The umbrella organisation is the charity of the year for the 2017 London Marathon, and Heads Together says it wants to use this privileged position to further tackle the stigma surrounding mental health.