Watch: Paul Burrell hopes Prince William and Prince Harry call a truce
Prince William and Prince Harry are "simply not talking at the moment" and have been doing everything through their teams in the run-up to the unveiling of the statue of their mother.
Biographer Omid Scobie told Good Morning America the relationship between the two princes is "extremely complicated" but that the event on Thursday afternoon, on what would have been Diana's 60th birthday, gives them an opportunity to talk.
He said: "The relationship between Harry and William is still extremely complicated.
"From what I understand from sources it is just a case of distance. They're simply not talking at the moment and while there has been small communication leading up to this point through their relevant teams, this is really going to be the first time where they have a proper opportunity to chat to each other."
He said being "in the presence of their mother" might be an opportunity for them to "remember the importance of love".
Scobie co-wrote last year's biography Finding Freedom which detailed the relationship between Meghan and Harry and their decision to step back. He said he did not interview either of the couple for the book but spoke to friends and sources close to them.
The royal brothers had always been very close growing up and rumours of their rift have dogged them for a number of years, with reports it began when Harry was dating Meghan.
However they stood shoulder to shoulder on Harry's wedding day, with William as best man.
Harry, 36, and Meghan decided to step back as senior royals in January 2020, beginning a trial year in March and then confirming their choice to leave their roles in February 2021.
In subsequent interviews Harry has said his brother and father, Prince Charles, are "trapped" in the royal system, and that there was a "cycle of pain and suffering" in his childhood.
He called the relationship with William "space" suggesting they were not in frequent contact.
The Times reported earlier this year that William and Harry argued while the Sussexes were still senior royals after bullying allegations were made about Meghan. She has denied them.
Meghan, 39, has not been back to the UK since March 2020, because of the coronavirus pandemic and her pregnancy. She had to miss the funeral of the Duke of Edinburgh and could not fly over for the statue unveiling because she only recently gave birth to daughter Lilibet.
Harry did attend his grandfather's funeral, and he was seen speaking to William after the ceremony, a conversation that appeared to be engineered by Kate, William's wife.
However reports following the funeral suggested the conversation did little more than "break the ice" and did not solve any of the issues between them.
True Royalty TV founder Nick Bullen said in May: "All of my sources tell me that they are not talking at the moment."
The brothers are said to be preparing to meet after the ceremony, which will be a small occasion, attended by Diana's siblings, the sculptor and the gardener, Pip Morrison, and limited media.
Earlier on Thursday, Paul Burrell, Diana's former butler, urged the brothers to reconcile, saying: "If this poignant day doesn’t do it, then nothing will because if they stand there in front of their mother’s image and just think and consider what she would have wanted and what she would have said to her boys, then they will know the answer to that question."
Watch: Tributes placed at Kensington Palace on day Princess Diana would have turned 60