Kate Middleton is one tough cookie.

Royal expert Valentine Low exclusively told Page Six in a recent interview that the Royal, 41, is “tougher” than she lets on.

“Interestingly, behind the scenes, she’s a lot more steely, a lot tougher than we give her credit,” he said.

“She’s this nice-looking woman, dresses nicely, smiles nicely, adopts sort of fairly uncontroversial charities,” the author explained.

“You know, they think she’s slightly bland.”

Low said one example of the Princess of Wales’ steeliness occurred after Prince Harry and Meghan Markle’s bombshell interview with Oprah Winfrey, which aired in March 2021.

In the candid sit-down, the “Suits” alum, also 41, shared that she had harbored suicidal thoughts during her brief stint as a working royal. The Duke of Sussex, 38, also implied that the monarchy had become jealous of Markle after seeing how popular she was on the couple’s first tour to Australia.

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The Duchess of Sussex also alleged that Middleton was the one who made her cry over flower girl dresses for her 2018 wedding to Harry — and not the other way around, as previously reported.

Most disturbingly, Markle — who is biracial — alleged that while she was pregnant with her son, Prince Archie, an unnamed member of the royal family raised concerns over “how dark his skin might be when he was born.”

The Palace waited until the interview aired in the UK to issue a response and Low says in a new chapter for the paperback edition of his book “Courtiers,” that there the royal family split on how to respond.

“The whole family is saddened to learn the full extent of how challenging the last few years have been for Harry and Meghan. The issues raised, particularly that of race, are concerning,” the statement from Queen Elizabeth II read at the time.

“While some recollections may vary, they are taken very seriously and will be addressed by the family privately.”

Low said that Jean-Christophe Gray, Prince William’s newly appointed private secretary, came up with the memorable line, “recollections may vary” in the statement, implying that the Palace disagreed about what had happened.

“There were some people in other [royal] households, who felt it would antagonize Harry and Meghan and would go down badly and just keep the whole unpleasantness going,” Low explained.

“But it was Kate who really strongly made the argument,” he noted, adding that the mom of three wanted that line to stay in the statement so that Markle and Harry’s version of events wouldn’t be accepted as truth.

Low told us that Middleton is acutely aware that “she’s one day going to be Queen” and “thinks very carefully about the long-term security and strength and stability of the royal family as an institution.”

He added, “She’s good. She has a good eye on the big picture, the long game.”