Royal family fun!

Kate Middleton, Prince William and Prince Harry are the stars of a newly released video promoting their latest charity campaign, Heads Together, which aims to end stigmas surrounding mental health.

"Mental health is just as important as physical health," Kate, 34, said in the clip, to which Harry, 31, added, "We can all play our part by talking and listening to each other and helping each other find support."

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The best part of the video? At the end, the trio — clad in matching, blue Heads Together headbands! — try to take a "serious" photo for the campaign, but can't stop laughing!

Watch the cute clip below!