Kate Middleton found the Windsor walkabout she and Prince William did with Prince Harry and Meghan Markle after Queen Elizabeth’s death last year to be “one of the hardest things” that she has done in her life, a new book claims.

The Princess of Wales, 41, and her husband famously greeted well-wishers outside Windsor Castle with Harry and Meghan on Sept. 10, just two days after the Queen died at age 96.

But rumors of a possible reunion between the two couples – who have been estranged since Harry and Meghan decamped for America in 2020 – were largely exaggerated, royal correspondent Robert Jobson writes in his new book, “Our King.”

“Catherine later admitted to a senior royal that, such was the ill feeling between the two couples, the joint walkabout was one of the hardest things she’d ever had to do,” Jobson states in an excerpt obtained by the Daily Mail.

Jobson’s book suggests that the joint outing was proposed by Prince William, 40, in an attempt to present a united front after the long-reigning Queen’s death – but any renewed closeness inevitably crumbled after the high-profile funeral services.

Just a few months later, Prince Harry took swipes at his brother and sister-in-law in Netflix’s “Harry & Meghan” documentary series.

Referring to the other men in the royal family, Harry, 38, said there can be a temptation or an urge to marry someone who would “fit in the mold” as opposed to somebody who you perhaps are “destined to be with.”

Markle also recounted her awkward first meeting with William and Kate, and suggested that the straight-laced pair rebuffed her warm advances.

Then, in January, Harry’s bombshell memoir “Spare” hit shelves and laid bare even more details of the couples’ rocky relationship.

In addition to alleging that William and Kate “howled with laughter” at his infamous Nazi costume, Harry also suggested that the then-Duchess of Cambridge was less than welcoming to Meghan.

During one tense moment, the red-headed royal recalled, Kate balked at the idea of lending Meghan her lip gloss.

Despite the obvious frostiness between the couples, royal watchers may see yet another reunion at King Charles’ coronation, which is set for May 6.

After months of back-and-forth, plans for Harry and Meghan to fly from California to London for the milestone event are reportedly “being finalized.”

“Harry has a lot of questions about how the event will work,” a source close to the Palace told Page Six this week.