The Duke of Cambridge says the Heads Together campaign was an experiment.
Prince William, 34, teamed up with his wife Duchess of Cambridge and brother Prince Harry for the campaign to raise awareness of mental health issues, and he claims it was the first time the three members of the Royal Family had focused on one thing together.
Speaking to GQ Magazine, Prince William said: "It is a bit of an experiment really. The Royal Family has not normally done this, three members of the family pulling together to focus on one thing.
"Normally things are quite disjointed, we follow our own interests and see where it goes, but we thought, well, if we tied it together and had a focused approach, how would that work?
"We wanted to see the impact we could have. We are all three of us trying to understand the tentacles of mental health which go everywhere."