Prince William, Prince Harry, Duchesses Kate and Meghan come together for cause

Princes William and Harry and Duchesses Kate and Meghan have come together again to collaborate on a short film for a cause close to their hearts: mental health.

William and Kate, the Duke and Duchess of Cambridge, and Harry and Meghan, the Duke and Duchess of Sussex, take turns narrating the minute-long film produced for a new mental health initiative called Every Mind Matters.

"Everyone knows that feeling when life gets on top of us. We feel stressed, low, anxious or have trouble sleeping. We think there's nothing to be done, nothing we can do about it," the royals say in the film. "But now, there's a new way to help turn things around."

The voices of Kate and Meghan are heard as they explain more about Every Mind Matters, an online tool designed to help people create a personalized action plan of self-care solutions. The initiative is backed by the U.K. government and a coalition of mental health charities including Heads Together, the mental health initiative started by William, Kate and Harry in 2016, before Harry and Meghan wed.

"We can all benefit from taking simple steps to look after our mental health," William says at the end of the PSA, which also includes a cameo from actresses Glenn Close and Gillian Anderson.

The PSA was written and produced by Richard Curtis, the director of "Notting Hill" and "Love Actually." Curtis visited William and Kate at Kensington Palace and Harry and Meghan at Frogmore Cottage in early September to have them each record their audio, according to ABC News royal contributor Omid Scobie.

The Every Mind Matters initiative marks the first time the four royals have collaborated publicly since June, when Harry and Meghan announced they were leaving the Royal Foundation, the charitable organization they shared with Prince William and Kate, to establish their own charitable foundation.

Harry and Meghan's Sussex Royal organization is expected to be up and running in 2020.

It is no surprise, though, that mental health is the cause that brought William and Kate, the parents of three, and Harry and Meghan, new parents to baby Archie, back together.

The royals have been outspoken advocates of increasing mental health awareness and breaking the stigma of mental health since launching Heads Together in May 2016.

William and Harry have spoken very candidly since then about the loss of their mother, Princess Diana, in 1997 and how it has affected their mental health in the years since.

"I have probably been very close to a complete breakdown on numerous occasions when all sorts of grief and sort of lies and misconceptions and everything are coming to you from every angle," Harry said in a 2017 interview in which he credited William with encouraging him to seek help. "For me personally, my brother, you know, bless him, he was a huge support to me. He kept saying, 'This is not right, this is not normal, you need to talk to [someone] about stuff, it's OK.'"

Harry and Meghan have made talking about mental health a focus of their first two official overseas tours as a couple, in Australia last year and in South Africa this month.

The couple joined surfers in Cape Town, South Africa, on Sept. 24 to talk about mental health, revealing they both practice meditation to help keep their mental health strong.