The Duke and Duchess of Cambridge, along with Prince Harry, will take a ride on the London Eye on Monday as they mark World Mental Health Day.
The trio will spend the day talking to those who have fought psychological problems - and hear about the help they have received.
At a reception in London, the young royals will meet those whose lives were changed thanks to support from a friend, colleague, or relative.
Guests will be able to take selfies in a special photo booth in County Hall with a message thanking someone for being there for them.
Kensington Palace said the Duke, Duchess and Harry were interested in learning about which support is most effective, as they explore future projects through the Heads Together initiative.
Heads Together, which is led by the three royals, aims to change the national conversation on mental wellbeing and is a partnership between charities that help with frontline mental health support.