Amazon boss Jeff Bezos has claimed the National Enquirer's parent company threatened to publish "intimate" photos of him, unless his private investigators backed off the newspaper.
The chief executive said he was the target of "extortion and blackmail" by the US tabloid's publisher, American Media Inc (AMI).
In a statement on Friday, AMI said it would 'promptly and thoroughly' investigate the claims made by the Amazon founder.
It comes after Mr Bezos - the richest person in the world - hired a team of private investigators following a story published by the newspaper detailing his extramarital affair.
He wanted to find out how journalists had got hold of "intimate texts" between himself and former TV anchor Lauren Sanchez.
According to an e-mail included in a blog post written by the 55-year-old entrepreneur, the publication had several revealing photos of Mr Bezos and Sanchez.
The newspaper's editor Dylan Howard appeared to have e-mailed a lawyer for the Amazon chief's security consultant earlier this week describing the photos, which Mr Howard said was "obtained during our newsgathering".
He said they included a "below the belt selfie" of Mr Bezos and a "naked selfie in a bathroom" in which the billionaire "is wearing nothing but a white towel".
"He's wearing either tight black cargo pants or shorts - and his semi-erect manhood is penetrating the zipper of said garment," he added in the e-mail describing another photo.
Lauren Sanchez, girlfriend of Jeff Bezos, arrives to the American Music Awards in November 2010 in Los Angeles | Image: Javier Rojas/Pi/Zuma Press/PA Images
The e-mail also stated there was a photo of Sanchez "wearing a two-piece red bikini with gold detail dress revealing her cleavage".
In further e-mails posted by the Amazon chief, a lawyer for AMI offered a deal on Wednesday, saying the Enquirer would not publish the photos if he and his investigators released a statement "affirming that they have no knowledge or basis" to suggest the paper's coverage was "politically motivated".
The investigators working for the billionaire tycoon, who bought The Washington Post in 2013, have suggested the Enquirer's coverage of his affair was politically motivated.
US President Donald Trump has hit out at Mr Bezos in the past over the Post's critical coverage of the White House, with AMI previously admitting it used "catch-and-kill" practices to help Mr Trump win the presidency.
The Enquirer reported last month that Mr Bezos had sent "sleazy text messages and gushing love notes" to Ms Sanchez in the months before he announced he was splitting from his wife MacKenzie.
Jeff Bezos. Picture by: Regina Wagner/Geisler-Fotopress/DPA/PA Images
Journalists followed Mr Bezos and Ms Sanchez "across five states and 40,000 miles" and "tailed them in private jets, swanky limos, helicopter rides, romantic hikes, five-star hotel hideaways, intimate dinner dates and 'quality time' in hidden love nests", according to its story.
Writing on Thursday, Mr Bezos said he decided to publish the e-mails sent to his team "rather than capitulate to extortion and blackmail" and despite the "personal cost and embarrassment they threaten".
AMI, meanwhile, said in a statement: "American Media believes fervently that it acted lawfully in the reporting of the story of Mr Bezos. Further, at the time of the recent allegations made by Mr Bezos, it was in good faith negotiations to resolve all matters with him.
"Nonetheless, in light of the nature of the allegations published by Mr Bezos, the Board has convened and determined that it should promptly and thoroughly investigate the claims. Upon completion of that investigation, the Board will take whatever appropriate action is necessary."