Prince William and Prince Harry have paid tribute to their mother Diana, Princess of Wales on the eve of the 20th anniversary of her death.The Princes were joined by the Duchess of Cambridge on a visit to the White Garden at Kensington Palace, which has been planted in memory of the late Princess at her former home.Head Gardener Sean Harkin led the tour and explained the design and planning of the garden, which features a number of Diana's favourite plants and flowers.The royals also met with representatives from some of the main charities the Princess supported in the final years of her life, including Great Ormond Street Hospital, the National Aids Trust, The Leprosy Mission and Centrepoint. According to Harkin, Diana was particularly fond of the Sunken Garden, where the White Garden is now based. Speaking about the design, he said he was inspired by has by memories of her life, image and style such as her white "Elvis" Catherine Walker dress, which is currently on display in the Diana: Her Fashion Story exhibition inside the Palace."Diana wore a lot of white and creams," Harkin told Country Living. "Certain pieces in the exhibition stood out - like the famous Elvis dress as well as some of the photos from the Mario Testino shoot in 1997 where she wore cream. The whole feel of the exhibition was radiant and uplifting which is what we wanted the garden to be."Key flowers in the garden include lilies, forget-me-nots, daisies and pots of white roses, which surround the reflective pool in the centre. After months of planning, Harkin said the royal brothers are thrilled with the result. "They have been supportive of the garden and are really happy we're doing something that celebrates her legacy," Harkin added.