Meanwhile, Prince William appeared to ignore a question when asked about the memoir in the U.K.
Kate Middleton feels "hurt and disappointed" with all the bombshell revelations Prince Harry made in his memoir, Spare.
A royal insider tells ET that the Princess of Wales feels that way because she believes "private matters had been made public." What's more, the royal insider says Middleton's disappointment is accentuated by the fact Harry had always described his sister-in-law as the sister he never had, but in Spare he acknowledges that his wife, Meghan Markle, and Kate's relationship never really took off.
Another source who knows both couples tells ET that "the relationship has completely broken down" between them.
Meanwhile, Prince William and Kate have put forth "a united front" in their first public engagement, and it's "business as usual" since Prince Harry's explosive biography dropped earlier this week, another source said. Both King Charles' office and Kensington Palace are not commenting and remaining silent in the wake of the bombshell allegations.
William and Kate on Thursday visited Merseyside in North West England to chat with those working at healthcare and mental health support services in the county. It was during that visit when a reporter called out to the couple, asking if William was hurt by the comments in Harry's book. It's unclear whether the Prince of Wales heard the question over the powerful winds.
Among the slew of bombshell allegations in Spare includes Harry claiming his older brother physically attacked him at his London home in 2019, after William allegedly called Meghan "difficult," "rude" and "abrasive." In an interview with ITV's Tom Bradby that aired over the weekend, Harry opened up about why he didn't fight back.
The Duke of Sussex, who said he and William used to "fight all the time like a lot of siblings," said he would have 100 percent fought William in the heat of that alleged 2019 altercation had it not been for therapy.
"I can pretty much guarantee today, that if I wasn’t doing therapy sessions like I was and being able to process that anger and frustration, that I would’ve fought back, one hundred percent," Harry told Bradby.
In an excerpt read from his autobiography, Harry read, "Come on, hit me, you’ll feel better if you hit me…Come on, we always used to fight, you’ll feel better if you hit me."
"No, only you’ll feel better if I hit you. Please, just leave," Harry said he replied.
In a 60 Minutes interview that aired on the same day, Harry said the alleged physical fight was a buildup of frustration.
Royal expert Katie Nicholl told ET that William is "incredibly angry at the level of detail" Harry went into for his headline-grabbing memoir.
"Knowing how bad things have got between the brothers, it's not actually all that surprising that one of them just lost their temper and lashed out," she told ET. "But to read about it in such detail is very painful, and one can only imagine very difficult for the Prince of Wales, Prince William, who of course isn't really able to answer back, isn't really able to share his side of the story."
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