Princess Diana William and Harry Remember Mom At Memorial Garden

8/30/2017 2:10 PM PDT

Princes William and Harry Visit Princess Diana's Memorial Garden on Eve of Death Anniversary

Prince William and Prince Harry honored Princess Diana by visiting a new garden dedicated to her ... where members of the public had already left tributes and flowers for their mother.

Catherine, the Duchess of Cambridge, joined her husband and Harry at the White Garden at Kensington Palace in London Wednesday ... on the eve of the 20th anniversary of Diana's death.

The trio toured the grounds -- formerly known as the Sunken Garden -- to pay tribute to the Princess of Wales ... who died in a car accident in Paris on August 31, 1997. William and Harry were 15 and 12 at the time.

The White Garden -- inspired by memories of Princess Di -- has been open since spring and includes some of her favorite plants.