The Woman in the Window was published in January 2018, and debuted at number on the New York Times best-seller list. Before its release, Mallory had worked as a book editor at publishing houses in London and New York.
According to the New Yorker, Mallory – a 39-year-old American who studied at Oxford University – allegedly told several colleagues that he had been diagnosed with brain cancer, and also included the claim in a university application.
The article also accused Mallory of telling people that his mother had died of cancer, and that his brother also died. While Mallory's mother did have cancer when he was a teenager, she and his brother are both alive.
Responding to the article with a statement at the end of the investigation, he wrote: "It is the case that on numerous occasions in the past, I have stated, implied, or allowed others to believe that I was afflicted with a physical malady instead of a psychological one: cancer, specifically.
"My mother battled aggressive breast cancer starting when I was a teenager; it was the formative experience of my adolescent life, synonymous with pain and panic. I felt intensely ashamed of my psychological struggles – they were my scariest, most sensitive secret."
Mallory claimed he was "utterly terrifed" of what people might think of him if they knew about his mental health problems. "Dissembling seemed the easier path," he said.
"Like many afflicted with severe bipolar II disorder, I experienced crushing depressions, delusional thoughts, morbid obsessions and memory problems. It's been horrific, not least because, in my distress, I did or said or believed things I would never ordinarily say, or do, or belive – things of which, in many instances, I have absolutely no recollection.
"With the benefit of hindsight, I'm sorry to have taken, or be seen to have taken, advantage of anyone's goodwill, however desperate the circumstances; that was never the goal."
Mallory's agent confirmed the statement to BBC News, while a spokesperson for HarperCollins UK told The Bookseller: "We don't comment on the personal lives of our employees or authors. Professionally, Dan was a highly valued editor and the publication The Woman in the Window – a Sunday Times best-seller, speaks for itself."
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