Prince Harry pushed his sister-in-law Kate Middleton to her “limits” with his bombshell BBC News interview last May, in which he discussed the health of his estranged father, King Charles III.

“The damage was done: seeds of doubt concerning the King’s chances for a full recovery had been sown,” royal expert Christopher Andersen writes in an excerpt from his upcoming novel, “Kate! The Courage, Grace, and Power of the Woman Who Will Be Queen,” obtained by Us Weekly.

During the shock interview Harry said he didn’t know “how much longer my father has,” which made Middleton “more disappointed than angry,” per the excerpt.

“Princess Catherine is ‘the sweetest, most loving person you could ever know,’ said a Sandringham staffer, ‘but like everyone else, she has her limits,’” another of Andersen’s excerpt reads.

At the time, Harry, 41, was referring to his father’s cancer diagnosis in February 2024. In the years since, Charles has undergone cancer treatment and given positive updates on his health.

Andersen also told Us Weekly Harry’s interview really struck a nerve with Middleton, who went through her own cancer battle and really bonded with Charles, 77, because of it.

“I think Kate’s relationship with her father-in-law over their shared cancer battles really has made her much more sensitive to King Charles’s feelings,” Andersen explained. “She knows better than anyone that having someone publicly imply you may be at death’s door is horribly demoralizing.”

“I’m sure Kate must have felt stung by that comment as well, since she is in a situation very similar to the king’s,” he added.

Anderson noted that Middleton, 44, has always been the “level-headed one” in the family feud and attempted to “bridge the widening gap between the brothers,” but Harry’s comments about Charles changed her stance. Afterward, she fully sided with her husband, Prince William, who was allegedly furious over his brother’s interview.

“But William, who had already slammed the door shut on his brother over what Harry wrote in ‘Spare,’ was, in the words of a courtier, ‘apoplectic’ with rage,” he writes in an excerpt. “Now it was time to nail the door shut once and for all, and for the first time Kate, who had worked harder than anyone to mend the rift between the brothers, willingly handed her husband a hammer.”

Andersen told the outlet he doesn’t see Harry and Middleton “having any sort of relationship” going forward. “At least not for the foreseeable future,” he added.

Page Six has reached out to reps for Harry and Middleton for comment.

Harry has been on the outs with his father and older brother since he and his wife, Meghan Markle, resigned from their royal duties in January 2020.

The couple ultimately moved to Montecito, California, where they live with their two children: Prince Archie, 6, and Princess Lilibet, 4.

Harry went on to drag his royal family members in several interviews as well as in his 2023 memoir, “Spare.” However, the Invictus Games founder has since shared his desire to reconcile with the reigning monarch.

“Kate! The Courage, Grace, and Power of the Woman Who Will Be Queen” releases May 5.