The Diana Award charity, named after the late Princess Diana, aims to “foster, develop and inspire positive change in the lives of young people”. It provides mentoring programmes for disadvantaged children and runs an initiative aimed at combatting bullying.
In an open letter to the charity Prince William said: “I wanted to write to send my support and thanks to all the staff, volunteers and supporters of The Diana Award.
“My brother and I remain ever appreciative of the work you do to foster, develop and support young people, particularly at this time of uncertainty.
“Whilst you are finding yourselves adapting to new ways of working, there is no doubt that your support for young people, through what will be anxious and unsettling times for many, is as important as ever.
“This comes with my very best wishes for good health to you and your families over the coming weeks.”
The post was accompanied with past photographs of Prince William and Prince Harry supporting the charities work, including at an awards ceremony.
Prince Harry is currently living in Los Angeles with his wife, Meghan Markle.
The couple shocked the world in January by announcing their intention to stand down as senior members of the royal family.
Instead the Duke and Duchess said they would seek to become “financially independent” whilst splitting their time between North America and the UK.
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“We’re incredibly grateful for all of our supporters (including you reading this right now) for making it possible for us to help young people change the world.
“We hope this brightens your day – it certainly did ours!”
The relationship between Prince William and Prince Harry has reportedly cooled over recent years.
Harry discussed the subject during ‘Harry & Meghan: An African Journey’, a documentary released last year covering a tour the couple did of Africa.
He stated: “We are brothers. We will always be brothers.
“We are certainly on different paths at the moment but I will always be there for him as I know he will always be there for me.
“We don’t see each other as much as we used to because we are so busy but I love him dearly.
“As brothers, you know, you have good days, you have bad days.”
The open letter was warmly welcomed by a number of The Diana Awards Instagram followers.
One said: “Harry is an incredibly wonderful and beautiful soul, he is his mother’s son.”
Another added: “Prince William is such an advocate for his mother’s legacy. He loves her so much and is carrying on paying tribute to her in his own way.”