William and Kate stepped out in Liverpool, England, but did not issue a public comment on Harry's memoir, in which he details an ongoing rift with William, including claiming that William physically attacked him in a 2019 confrontation.
As William and Kate arrived at a local hospital, a reporter shouted to William, "Are you going to comment on Harry's book, sir?"
Neither William nor Kate acknowledged the reporter's question as they stopped for a brief chat with others before entering the hospital.
Charles also did not publicly comment on his son's memoir, maintaining the royal family's silence on its contents.
Neither Kensington Palace, the office of William and Kate, the Princess of Wales, nor Buckingham Palace, the office of Charles and Camilla, the Queen Consort, have commented on the claims Harry makes in "Spare."
The memoir, a rare glimpse of life inside the royal family, became an instant bestseller upon its release Tuesday, selling over 1.4 million copies in the United States, United Kingdom and Canada alone in its first day, according to the book's publisher, Penguin Random House.
The company, which describes itself as the "world's largest trade publisher," said in a statement Wednesday the sales of "Spare" made history as the, "largest first-day sales total for any nonfiction book ever published by Penguin Random House."
"Spare" gives a detailed account of Harry's rift with his family, his decision to leave his senior royal role in 2020 and how he felt growing up as the "spare" to William, the heir to the throne.
Harry has said in interviews promoting "Spare" that he is not in regular communication with his brother or his father.
Harry and his wife Meghan, the Duchess of Sussex, who now live in California, last appeared in public with William and Kate in September when they attended Queen Elizabeth II's funeral. The mourning period for the queen marked the first time the couple had appeared publicly with members of the royal family in over two years.
Though Harry in his memoir shares intimate, often painful portrayals of the royal institution and his family, he told "Good Morning America" co-anchor Michael Strahan that telling his story is what is needed to make peace.
"I don't think that we can ever have peace with my family unless the truth is out there," he said in an interview that aired Monday on "GMA." "There's a lot that I can forgive, but there needs to be conversations in order for reconciliation, and part of that has to be accountability."
Harry also told Strahan he does not believe the details he shares in "Spare" can make things any worse with his family.
"I have thought about it long and hard," Harry said. "And as far as I see it, the divide couldn't be greater before this book."
ABC News reached out to Kensington Palace and Buckingham palace for response to Harry’s remarks in our interview. Kensington Palace declined to comment.
ABC News received a response from the law firm representing Buckingham Palace Monday saying that the palace needed to "consider exactly what is said in the interview and the context in which it appears," and asked that we supply them immediately with a copy of the entire interview. We do not do that as a news organization as a matter of policy.