Prince William and his younger brother Prince Harry were once close siblings at the center of the British royal family.

However, their relationship has since soured in the past few years, plagued by Harry’s claims in his book “Spare” as well as his 2020 move to California with his wife, Meghan Markle.

Christopher Andersen, author of “The King,” alleges that the Prince of Wales, 41, is still fuming over Harry’s 400-page memoir.

“William is still simmering with resentment over ‘Megxit,’ not to mention Harry’s unflattering portrait of him in ‘Spare,’” the royal expert claimed to Fox News recently.

Andersen went on to note what the Duke of Sussex, 38, had penned about William, reiterating that Harry portrayed him as his “arch-nemesis.”

In the book, Harry also alleged that he was left bruised after William flung him to the floor following a fight they had two months before he and Markle, 41, left the royal family.

The Duke of Cambridge reportedly called the former “Suits” actress “difficult,” “rude” and “abrasive” at the time.

Harry then fired back that he was only trying to combat the negative press the couple had endured.

“Harry is still obviously upset that William was given a free ride because he is the heir – that William got away scot-free with doing many of the same things Harry was excoriated for,” Andersen claimed.

“William is doing a marvelous job of compartmentalization. He seems to have put Harry and Meghan in a box and shoved that box into a remote corner of his mind.”

Andersen asserted that William is just trying to “do the job he must do as Prince of Wales.”

“Spare” was published by Penguin Random House this past January and is full of bombshell anecdotes about his life as the “spare” sibling in the royal family.

Other tidbits include his feelings towards his mother Princess Diana’s untimely 1997 death and his attitude towards his stepmother, Queen Camilla.

During a promotional tour for his book, Harry appeared on “Good Morning America” and had a one-on-one interview with anchor Michael Strahan.

The father of two got candid about why he branded William as his enemy and further explained his stance.

“There has always been this competition between us, weirdly,” Harry said. “I think it really plays into — or is played by — the ‘heir, spare.’”

Harry added that Diana would be devastated about the estranged relationship between him and his brother.

“I think she’d be sad,” he sighed. “I think she would be heartbroken that it’s ended up where it’s ended up.”