Prince Harry's blockbuster memoir "Spare" is already a runaway success, shattering sales records as readers rush to learn details both salacious and mundane about the British royal's life. 

Though the 38-year-old has been on a media blitz promoting his book in recent weeks, the prince had help piecing together the 416-page manuscript for "Spare" in the form of superstar ghostwriter J.R. Moehringer, who has quietly written a number of other bestselling autobiographies. 

Ghostwriters are writers who pen books on behalf of another party, usually without publicly receiving credit. In the case of "Spare", Moehringer's name does not appear on the cover and the book is attributed solely to Prince Harry. 

Though he has not done any press for "Spare", Moehringer has opened up about the ghostwriting process in the past. 

He has ghostwritten two other bestselling autobiographies: 2009's "Open" for American tennis star Andre Agassi and 2016's "Shoe Dog" for Nike founder Phil Knight. Additionally, in 2005 he penned his own memoir, "The Tender Bar", which was adapted into a 2021 film starring Academy Award winner Ben Affleck. 

In the case of Agassi's memoir, Moehringer told the New York Times in 2009 that he spent 250 hours with the 8-time Grand Slam champion in sessions that "sometimes resembled psychoanalysis." But the end result allowed him to more accurately capture Agassi's voice and tell his story.

"You try and inhabit their skin, and even though you're thinking third person, you're writing first person, so the processes are mirror images of each other, but they seem very simpatico," he said in a 2012 interview on NPR's "Fresh Air". 

Moehringer told the Times he was adamant that his name not appear on the cover or title page, a practice he continued for both "Shoe Dog" and "Spare". 

"The midwife doesn't go home with the baby," he explained. "It's Andre's memoir, not our memoir, not a memoir 'as told to.' It's his accomplishment, and he made the final choices."

"Spare" has made headlines thanks in part to a number of accusations that Prince Harry made against the royal family, including that his brother Prince William physically attacked him during an argument about his marriage.

The memoir, which was released Jan. 10, is currently the No. 1 book on Amazon's best seller list.

A representative at "Spare" publisher Penguin Random House did not immediately respond to a request for comment.

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