“In updating this story, I am saddened about the depth of the rift and the animosity between the two of them,” Lacey tells PEOPLE in this week’s issue.

Lacey wrote the first edition of the book last year but has spent the time since updating it and adding more chapters.

At the same time, says Lacey, “I have also come to feel there are solid, long-term reasons for this being resolved in the future.”

Prince Harry and Prince William.Andrew Milligan/Getty

royal wedding 2011

One of those moments for a step towards reconciliation may come next week when the brothers are united at theunveiling of a statuededicated to their late motherPrincess Diana, who would have been 60 on July 1.

Prince Harry and Prince William.Tolga Akmen - WPA Pool / Getty Images

Prince Harry and Prince William sussex cambridge

According to some of Lacey’s new chapters, things worsened again in October 2018 when William, 39, learned of allegations fromstaffers who said they had been bullied. (When the bullying claims first surfaced inThe Timesin March, the Duchess of Sussex’s officestrongly denied the allegationsand said they were part of a smear campaign against the Duchess, 39. The palace set up an independent inquiry, which is still “ongoing,” a source confirms.)

Can’t get enough ofPEOPLE’s Royals coverage?Sign up for our free Royals newsletterto get the latest updates onKate Middleton,Meghan Markleand more!

The tensions have also devastated members of the royal family — including their father,Prince Charles.

Prince William, Prince Charles and Prince Harry.Samir Hussein/WireImage

Prince Charles, Prince of Wales, Prince William, Duke of Cambridge and Prince Harry

The future king, 72, has historically had complicated relationships with his sons and is finding it hard to intervene as increasingly painful revelations about the roots of the brothers' discord continue to come to light.

source: people.com