It will be placed in the garden of the London palace on 1 July 2021.
The statue was commissioned by the princes in 2017 to mark the 20th anniversary of their mother's death and to "recognise her positive impact".
On Monday it will be 23 years since she was killed in a car crash in Paris.
Kensington Palace said installation of the sculpture had been delayed by the coronavirus pandemic, but it would be unveiled in the Sunken Garden next year.
It has been created by artist Ian Rank-Broadley, whose portrait of the Queen appears on all UK coins.
Further details of the design will be announced later, according to Kensington Palace.
When they announced the commission, the princes said they hoped the permanent sculpture would help all those who visited Kensington Palace to "reflect on her life and her legacy".
"Our mother touched so many lives," they said.
The Princess of Wales died on 31 August 1997, when Prince William and Prince Harry were aged just 15 and 12.
Several London memorials have been created in tribute to Diana, including the Diana Memorial Playground at Kensington Palace, the Diana Memorial Fountain in Hyde Park, and the Diana Memorial Walk at St James's Palace.
A memorial garden known as the White Garden was also planted at Kensington Palace to mark the 20th anniversary of her death.
Real Eyes. Realize. Real Lies.