The pair were accompanied on Wednesday afternoon by Prince William's wife, Catherine, the Duchess of Cambridge, as they toured what had been known as the Sunken Garden at Kensington Palace in London, to mark two decades on from the death of their mother Diana, Princess of Wales.
"The engagement will allow the Princes to pay tribute to the life and work of their mother the day before the twentieth anniversary of her death," an earlier statement from Kensington Palace said.
Diana died in a car accident in Paris on August 31, 1997, leaving behind her sons then aged 15 and 12 years old, as well as a philanthropic legacy that won her admirers the world over. She divorced her husband Charles, Prince of Wales, in 1996.
The White Garden is the result of a transformation that features several of the late princess's favorite plants and was inspired by her work, image and style, including her famous white "Elvis" Catherine Walker dress.
Open since spring this year, the garden contains white roses, lilies, gladioli and cosmos flowers. The transformed garden will continue into September.
The princes toured the garden, alongside the head gardener and another gardener who knew the Princess of Wales, before meeting representatives from several of the organizations Diana supported in the final years of her life as well several charities that she had a close relationship with.
Those attending the engagement in the White Garden included people from the UK's homeless charity Centrepoint, the National AIDS Trust, Great Ormond Street Hospital, the Leprosy Mission and the Landmine Survivors Network.
The royals invited them so they could hear about the impact of their mother's work, according to the official Kensington Palace Twitter account.
The White Garden is the fourth memorial to the popular princess since her death. The others are the Diana Memorial Playground, also at Kensington Palace, Hyde Park's Diana Memorial Fountain and the Diana Memorial Walk at St. James's Park.
Diana lived a life in the public eye, with every move photographed and scrutinized, and was beloved by many. Upon her death in 1997, a sea of flowers, cards and gifts were left by mourners at the gates of Kensington Palace.
Her legacy still resonates with the public, with well-wishers returning once again to leave messages of support and love.
This year's anniversary has been a more private affair for the family, in contrast to the celebrations William and Harry orchestrated to mark the 10th anniversary of Diana's death in 2007.
The pair held a tribute concert featuring Elton John and Duran Duran for Diana, who was a great fan of music and musical theater, at London's Wembley Stadium on what would have been her 46th birthday.
On the anniversary of her death a month later, a memorial service attended by Queen Elizabeth was held at the Guards' Chapel at Wellington barracks near Buckingham Palace.