WATCH: Royal Fab Four 'Break The UK Health Service Website' With New Ad

The Royal Family's 'Fab Four' have joined forces in a television-first, lending their voices to a UK mental health campaign.

More than ten million UK viewers tuned in to watch William, Kate, Harry and Meghan narrate a short film for the launch of the Every Mind Matters initiative -- Public Health England's new digital platform.

The three-minute ad, which is aimed at encouraging people to manage the early symptoms of poor mental health, was broadcast across multiple TV channels as part of a "national takeover".

It's the first time any of the fab four have appeared in a television advert.

After the ad's release, the UK's National Health Service website (that hosts Every Mind Matters) crashed as people rushed to view it online.

Actress Glenn Close appears in the video. Image: Every Mind Matters

The ad also features celebrity names including former cricketer Freddie Flintoff, actors Glenn Close and Gillian Anderson, and BBC presenter Nadiya Hussain.

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"Everyone knows that feeling when life gets on top of us," Prince William can be heard saying in the ad.

"All over the country, millions of us face challenges to our mental health - at all ages - at all intensities, and for all sorts of reasons.

"We feel stressed, low, anxious, or have trouble sleeping. Me, you..."

"Your brother, your mother, your colleague, or your neighbour," Prince Harry continues.

Meghan picks up where her husband leaves off, assuring viewers "there's a new way to help turn things around" when facing mental health struggles.

"Every Mind Matters will show you simple ways to look after your mental health," she says.

Kate wraps up by introducing the initiative's "mind plan", aimed to help those in need to learn to cope with stress, boost their mood and sleep better.

A UK public health survey of more than 3,000 adults, found that 83 percent  had experienced early signs of poor mental health in the last year.

More than a quarter of respondents waited longer than six months before addressing their mental health issues.

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge, Prince Harry, Duke of Sussex and Meghan, Duchess of Sussex. Image: Getty

The royal project is the first joint venture between the fab four since the quad split from their joint charity.

In May, Prince Harry and Meghan stepped away from The Royal Foundation -- a charity founded by William and Kate more than a decade ago.

Officials said the decision was a strategic one, and the two households would continue to work together on philanthropic projects.