The Duke and Duchess of Cambridge put their artistic skills on display as they visited a mental health event in London.
William joked that he and Kate might have “ruined” a picture being painted during the two-day Global Ministerial Mental Health Summit.
The royal couple both somewhat nervously added a single brushstroke to Dairo Vargas’ artwork after meeting people working to raise awareness of mental health issues around the world.
After picking up the paintbrush himself he then told the artist: “This is how you properly ruin a picture.”
When Mr Vargas invited the pair to add to the painting, Kate told him: “This is very brave of you.”
Describing the royal touch as “amazing”, he added: “I feel very excited and happy to be part of this project.”
William, who wore a dark suit, and Kate, wearing a lilac dress, were greeted by Health Secretary Matt Hancock as they arrived to cheers from crowds waiting in the street at County Hall.
Political figures, experts from around the world and policy makers are attending the event to discuss issues such as how to deal with the stigma attached to mental health.
William and Kate have long been involved in mental health initiatives through their Heads Together campaign.
They were reunited on Tuesday with Elisha London, who worked on that campaign, as they learned about a Zimbabwean project called the Friendship Bench.
Alexandra Almeida, from the My Mind Our Humanity campaign as part of the Lancet commission on global mental health, said it was “very nice” to meet William and Kate and have their support.
Ms Almeida, from Portugal, said: “They wanted to know if we feel there has been a change in mental health and how the young people view mental health in Britain and other places across the world.
The royals also met young people who have either had or are dealing with mental health issues and heard about case studies of mental health projects in the USA and India.
They were hosted during their visit by Sue Baker, director of Time to Change, and Professor Tim Kendall, national clinical director for mental health with NHS England.
A poll published this week showed that almost a quarter of patients with a mental health problem are waiting more than three months to see an NHS specialist.
The Royal College of Psychiatrists said that long waits for mental health care “have been deemed acceptable”.
The college has launched a new campaign urging medical students to become doctors who specialise in mental health.
Ahead of the summit, the Department of Health and Social Care began a social media campaign using the hash tag #TheWorldNeeds to ask people what needs to change in the way mental health is treated and perceived.