A lawyer for a detainee at Guantanamo Bay's highest-security section has rubbished reports that Fifty Shades of Grey is a favourite read among inmates.
A US congressman made the claim last month after visiting Camp 7, saying it showed the inmates were "not exactly holy warriors".
Lawyer James Connell says guards this week gave a copy of the erotic novel to his client, possibly as a joke.
But 9/11 accused Ammar al-Baluchi had no interest in the book, he said.
The 35-year-old, also known as Abd al-Aziz Ali, is a senior al-Qaeda member who has been charged with war crimes.
He is also a nephew of Khalid Sheikh Mohammed, the alleged mastermind behind the September 2001 attacks.
Mr Baluchi turned up in court this week at Guantanamo for pre-trial hearings, with a copy of E L James' best-seller, according to his lawyer.
"He said, 'you'll never guess what I have,'" Mr Connell told the BBC.
Mr Baluchi handed the copy of Fifty Shades of Grey to his lawyer, and said the fairly worn paperback had been a gift.
A couple of guards at Camp 7, the secretive facility where he is confined, had given him the book, Mr Baluchi said.
Mr Connell said his client has not read the book. He is an avid reader of the Economist and Wired magazine - and the novel did not interest him, said the lawyer.
"He [Mr Baluchi] knew that it was some sort of a joke," said Mr Connell. "Or some sort of disinformation campaign."
The book was passed to Mr Baluchi after reports circulated of its alleged popularity among inmates, following a US congressman's visit in July to the prison.
Journalists are not allowed to visit Camp 7, a secretive facility that opened in 2006.
But Representative Jim Moran, a Virginia Democrat, told the Huffington Post he had discovered that detainees in the facility were enjoying the trilogy of novels about sadomasochism.
"It demystifies them," Mr Moran also told the Miami Herald, following his 26 July tour of the base.
"It exposes them for who they actually are."
He said that their choice of reading material shows they are "not exactly holy warriors. Just the opposite. These people are phonies."
The claim surprised many as inmates' access to reading material is strictly controlled at Guantanamo Bay, and the racy book is not even thought to be in the prison's main library.
Commentators, including Miami Herald reporter Carol Rosenberg, were sceptical about Mr Moran's remarks. In her article, Rosenberg described the claim as "odd".
John Grisham, whose work is not nearly as steamy as Fifty Shades of Grey, wrote in a recent New York Times article that one of his books had been censored.
Pentagon spokesman Lt Col Todd Breasseale told the BBC: "I'm not going to dispute a detainee whose words are being relayed by his attorney. I'm not interested in disputing hearsay."
Mr Connell told the BBC his client has a sense of humour.
"He was more amused than offended," he said.
But Mr Connell said he plans to give the paperback to a top-level military lawyer with the Guantanamo Joint Task Force.
He is keeping the book, which he showed to a BBC journalist at a media-operations room, in a plain envelope.
"If this is a practical joke, it has gone too far," said Mr Connell.