Prince William and his brother Prince Harry say they spent years not talking enough to each other about the pain of losing their mother Diana, Princess of Wales.

In a newly released video, the Duke and Duchess of Cambridge, William and Catherine, sit down at a picnic table with Prince Harry to discuss candidly why they have made mental health the focus of their charitable work.

They say they’ve realized the value of “simple conversations” to begin the process of mental health healing, and admit they themselves spent many years not talking about the sudden death of their mother.

Asked by Catherine whether their strong family ties helped them to cope with the grief, William responds that he and his brother “are uniquely bonded” because of what they went through.

"But even Harry and I over the years have not talked enough about our mother," he added.

Prince Harry agreed, adding that working on the mental health campaign helped him to realize that.

"I always thought to myself, what's the point of bringing up the past, what's the point of bringing up something that's only going to make you sad? It ain't going to change it, it ain't going to bring it back," he said. "And when you start thinking like that, it can be really damaging."

The candid conversation is just the latest in a series of videos the young royals have released this month, to promote “Heads Together” The campaign, led by The Royal Foundation in partnership with eight British and international charities, aims to challenge the stigma of mental illness.

Earlier this week, Prince Harry revealed in a podcast interview that he sought counselling four years ago after coming close to a "complete breakdown" brought on by years of refusing to deal with his grief.

The following day, Prince William released a video in which he spoke with pop star Lady Gaga, via FaceTime, about why she decided to speak publicly about her own struggles with post-traumatic stress disorder.