In the pages of his memoir Spare last January, Prince Harry laid bare the terrible schism between himself and his family, and the public learned the magnitude of the schism between Harry, 39, and his brother Prince William, 41.

However, over a year after the publication of Spare, “absolutely nothing has changed,” author Omid Scobie, whose new book Endgame will be released on November 28th, tells PEOPLE in this week’s cover story.

Indeed, Scobie claims that the hurt and resentment between the two brothers—one, the Prince of Wales and future King, and the other, the Duke of Sussex and Californian—has solidified into something colder and more immovable: apathy.

“I saw Harry’s release of Spare as his last attempt at telling his family how he’s felt for years,” says Scobie, whose Endgame traces the collapse of the royal family as well as the crumbling of the modern monarchy. “Because clearly there’s never been an open enough forum to have these conversations or share these feelings.”

Of course, the royal family is not known for emphasizing emotions. But, as Scobie argues in Endgame, the royal family is disregarding its own divisions at its peril because “part of the buy-in from the [British] public is that the royal family is the nation’s family.” Nonetheless, heir-to-the-throne William, according to Scobie, has emphasized his allegiance to the monarchy, even secretly conspiring with the British press to damage Harry. (When PEOPLE contacted Kensington Palace about the claims, they had no response.)

While working on Endgame, “I was talking to a source quite early on in the process, and they called Harry a ‘defector’ and said that was William’s view,” Scobie adds. “Once upon a time, these were two men who shared a common outlook.” One of them had to go to preserve the crown.”

But will there be a crown to defend in decades to come? “There’s a real chance here to learn and adapt to modern society and also make up for mistakes of the past,” Scobie said. “It’s their move.”

Even if the monarchy survives, the issue of whether sacrificing fraternal relationships is worthwhile remains. “These are probably sad realizations that will be had far too late in the journey,” said Scobie. “In the eyes of some within the establishment, Harry poses a threat to the monarchy. “His freedom to think for himself outside of the institution has made him the adversary.”

That’s why, for the brothers, he adds, “There’s no going back.”