The statue was created to reflect Diana's "warmth, elegance and energy" and depicts her with children "who represent the universality and generational impact of the Princess' work," Kensington Palace said in an official statement.
"The portrait and style of dress was based on the final period of her life as she gained confidence in her role as an ambassador for humanitarian causes and aims to convey her character and compassion," the statement continued.
Diana died Aug. 31, 1997, from injuries after a car crash in Paris.
"Today, on what would have been our mother's 60th birthday, we remember her love, strength and character — qualities that made her a force for good around the world, changing countless lives for the better," William and Harry said in a joint statement. "Every day, we wish she were still with us, and our hope is that this statue will be seen forever as a symbol of her life and her legacy."
The princes thanked "all those around the world who keep our mother’s memory alive.”
The private event — only one videographer and one photographer were present — took place amid the widely reported tensions between the two brothers, particularly following Harry and his wife Meghan Markle's blockbuster interview with Oprah Winfrey in March. In the interview, Harry and Meghan claimed that the royal family ignored their requests for help and that one member had raised concerns about what skin color their child would have.
During the interview, Harry said he loved his brother "to bits," but that their relationship was "space at the moment, and you know, time heals all things, hopefully." Harry flew from his home in California to reunite with the members of his family on April 17 for the funeral of their grandfather, Prince Philip.
In accordance with coronavirus restrictions, attendance at the statue unveiling was limited to Diana's sons, close family members, members of the private statue committee that raised the funds for the project, sculptor Ian Rank-Broadley, and the heads of the design and planting teams who overhauled the Sunken Gardens, where the statue was placed.
The gardens were redesigned "to create a calmer and more reflective setting for the statue," according to an official press release. Work began in October 2019, and the new layout, designed by landscape architect Pip Morrison, features a number of Diana's favorite flowers, including forget-me-nots.
Historical Royal Palaces Deputy Head of Gardens and Estates Graham Dillamore, who led the redesign, worked on the gardens during Diana's lifetime.
"[She] regularly admired the changing floral displays in the Sunken Garden and would always stop to talk with me and the other gardeners who cared for it. Over three decades later, I’m honored to have been part of the team preparing the garden for the installation of this statue," he said.
The statue is engraved with Diana's name and the date of the unveiling. Beneath the statue is a verse from the poem "The Measure of a Man."
“These are the units to measure the worth
Of this woman as a woman regardless of birth.
Not what was her station?
But had she a heart?
How did she play her God-given part?”
William and Harry commissioned the statue in 2017 to mark the 20th anniversary of Diana's death. They said in an official statement that "the time is right to recognize her positive impact in the UK and around the world with a permanent statue."
"Our mother touched so many lives. We hope the statue will help all those who visit Kensington Palace to reflect on her life and her legacy."