The Duke of Sussex said “planting and leaking” by his family members resulted in “a million words” being written “trying to destroy my wife”.
In an interview with Tom Bradby on ITV, Harry said that he wrote his book Spare because of “38 years of … spinning and distortion”.
The memoirs, due to be published on Tuesday, contain a number of revelations – with Harry’s brother, the Prince of Wales, the subject of many of them.
Claims about William include that he physically assaulted Harry in 2019 and that he was “wasted” on hours of rum before the wedding.
Bradby asked the prince what his brother would tell him about the book.
“He’d probably say a lot of different things,” said Harry.
“But you know for the last however many years let’s just focus on the last six years the level of boosting and leaking from other family members means countless books have been written in my head sure millions of words have been spent trying to destroy my wife and me to the point that I had to leave my country.”
Harry said he chose to write his memoirs because he felt it was a good time to tell his story.
“(After) 38 years of my story being told by so many different people with deliberate distortion and distortion, (it) felt like it was a good time to own my story and be able to tell it for myself.
“You know, I don’t think if I was still part of the institution I would have had that chance.
“So I’m really grateful that I had the opportunity to tell my story because it’s my story to tell.”
In the past, the prince has complained about the media invasion of his private life.
Bradby asked him how he could now justify the amount of disclosure in the book.
“There was a motto, a family motto: ‘never complain, never explain,'” he said.
“And people have now realized, thanks to the Netflix documentary, the documentary, and the numerous stories that have surfaced over the years, that it was just a motto.
“There was a lot of complaining and a lot of explaining and it continues now.”
He said the “truth” now comes from his own mouth, not from the tabloids.
“But as far as I’m concerned, I’m sitting here right now, talking to you, answering the questions you ask me, and the words and the truth come from my mouth, not through other people, especially through the tabloids.
“And now we’re six years old, and I’ve spent every year of those six doing everything in my power to reach out to my family privately.”
Harry said it “never had to be that way” and that he had tried to talk to his family.
“And the saddest part of it all, Tom, is that it never had to be that way,” he added.
“You never had to get to that point. I’ve had conversations, I’ve written letters, I’ve written e-mails, and everything is just “no, that’s not what’s going on.” You imagine it.”
“And that’s really hard to bear. And if it had ended, to the point where I would have fled my home country with my wife and son in fear for our lives, maybe things would have turned out differently. It is hard.”
The ITV interview is the first of four appearances to be broadcast over the coming days, and the Duke also spoke to American journalist Anderson Cooper on 60 Minutes on CBS News, Michael Strahan from Good Morning America on Monday and Stephen Colbert on the Late Show on CBS Wednesday morning UK time.