Changes that the Duke of Cambridge and Duke of Sussex are said to have made to the design of a statue of Princess Diana are delaying its completion and display in Kensington Gardens.
Two years ago, the brothers revealed that they had commissioned the statue of their mother for the public part of their then Palace home, to commemorate 20 years since her death in Paris in 1997.
A Kensington Palace spokesman told The Mail on Sunday: "This is not a short-term project, this is a statue that will last for ever.
"It is about ensuring that this enduring monument is completely right."
The statue's sculptor, Ian Rank-Broadley, is most recognised for his depiction of the Queen, which has appeared on all coins in the UK and Commonwealth since 1998. He also designed a gold coin marking the Queen's diamond jubilee in 2012.
Princess Diana died at the age of 36 when the car she was travelling in crashed in a Paris tunnel on August 31, 1997.
Announcing the project in 2017, William and Harry said: "It has been 20 years since our mother's death and the time is right to recognise her positive impact in the UK and around the world with a permanent statue."