Prince Harry’s ghostwriter has said he bonded with his subject over the “callousness” of paparazzi and media after the “frenzied mob” around the book Spare led to photographers and journalists invading his own privacy.

In a first-person piece for the New Yorker, JR Moehringer, the celebrated ghostwriter behind Spare said he agreed to write Harry’s memoir because he “just liked the dude” and had recently lost his own mother.

“I wondered if we’d have any chemistry. We did, and there was, I think, a surprising reason. Diana, Princess of Wales, had died 23 years before our first conversation, and my mother, Dorothy Moehringer, had just died, and our griefs felt equally fresh,” he wrote.

“I think I selfishly welcomed the idea of being able to speak with someone, an expert, about that never-ending feeling of wishing you could call your mom.”

The book took over two years to write, with Moehringer and Harry meeting over Zoom during the pandemic and exchanging text messages “round the clock”. When travel restriction eased, Moehringer went to stay at a guesthouse on Harry and Meghan’s ranch in Montecito, California, where “Meghan and Archie would visit me on their afternoon walks. Meghan, knowing I was missing my family, was forever bringing trays of food and sweets.”

When news of the memoir leaked, writes Moehringer, “one royal expert cautioned that, because of my involvement in the book, Harry’s father should be ‘looking for a pile of coats to hide under’,” because of what Moehringer describes as his own “daddy issues”. He has written about his absent father and his close relationship with his single mother in his own memoir, The Tender Bar.

Spare went on to become the fastest-selling nonfiction book of all time. Its success also led to fevered media attention, and Moehringer recounts paparazzi and reporters starting to intrude on his personal life, following him in his car, showing up outside his son’s preschool and snooping around his home. “[…] I looked up to see a woman’s face at my window. As if in a dream, I walked to the window and asked, ‘Who are you?’ Through the glass, she whispered, ‘I’m from the Mail on Sunday’.”

With tabloid attention came errors and lies, he writes, where “innocent passages” were “hyped into outrages”. Among these was a mistranslation that led news outlets to report that Harry had described “mounting” the woman to whom he lost his virginity. “I can assert with one-hundred-per-cent confidence that no one gets ‘mounted,’ quickly or otherwise, in Spare,” he writes.

When he complained to Harry “fictions about me were spreading and hardening into orthodoxy” – among them that he had been introduced to Harry by George Clooney – the prince “tilted his head: Welcome to my world, dude. By now, Harry was calling me dude.”

In the New Yorker piece, Moehringer, who also worked as a ghostwriter for Andre Agassi and Nike founder Phil Knight, recounts pushing back on Harry’s request to include a comeback he made during a military exercise in which he was involved in a simulated kidnapping.

During the exercise, one of his pretend captors made a “vile dig” at Diana. Harry wanted his remark included because people had “belittled his intellectual capabilities” and he wanted to show that he had said something clever.

Moehringer refused, saying it would detract from the meaning of the scene, which was actually that, “even at the most bizarre and peripheral moments of his life, his central tragedy intrudes”.

Harry, he says, “couldn’t escape the wish that Spare might be a rebuttal to every lie ever published about him.”

The book included explosive details, including Harry taking drugs as a teenager, a scuffle between Harry and his brother, Prince William, fights between Meghan and the Princess of Wales over bridesmaids’ dresses, and the assertion that William and Kate were behind Harry’s choice of a Nazi costume at a 2005 fancy dress party.

He accused his family having “a huge level of unconscious bias” and said it failed to protect Meghan from attacks in the press. Harry travelled alone to his father’s coronation on 6 May, which was held on the same day as his son Archie’s birthday, and made a swift exit afterwards.

• This article was amended on 9 May 2023. Spare holds the record for the fastest-selling, not “bestselling”, nonfiction book as an earlier version said.