Prince Harry officially opened the London Marathon expo with a little help from a five-year-old girl.
The royal was making his first public appearance since he admitted he almost had a breakdown and had to seek counselling to come to the terms with the death of his mother.
This August will mark 20 years since Harry and his brother William lost their mother Princess Diana.
Five-year-old Melissa Howse helped Harry cut the ribbon - although she looked a little nervous as the prince held the scissors.
Her dad Tony said: "I don't think she knew who he was, but she was very, very excited."
From Wednesday to Saturday the majority of the more than 50,000 runners will attend the expo at London's ExCel Centre to collect their race numbers and final information ahead of Sunday's 26.2 mile race.
Heads Together, the mental health campaign spearheaded by Harry and the Duke and Duchess of Cambridge, is the 2017 London Marathon Charity of the year.
The mental health charity aims to encourage people to talk about their psychological problems or be a sympathetic ear for those in need.
Prince Harry handed out race numbers to some of the first runners across the line at the expo.
Every runner taking part in the April 23 event will receive a blue Heads Together headband.
They will also get a note from William, Kate and Harry wishing them luck and encouraging them, no matter which important cause they are running for, to help Heads Together make the event the mental health marathon.
Later on Wednesday, Kate will host marathon runners from team Heads Together at Kensington Palace, where she will chat to the group and discuss their reasons for taking part and wish them luck.
The runners will then take part in a training session with coach Nick Anderson.