David Pecker, the chief executive of American Media Inc., which publishes the tabloid National Enquirer, threatened to publish embarrassing photos of Jeff Bezos if he didn’t stop investigating Pecker’s company, according to the Amazon CEO.

Bezos revealed the alleged threat, which was sent through AMI chief content officer Dylan Howard, in a blog post published to Medium on Thursday. In it, Bezos also claimed that an “AMI leader” told him that Pecker was “apoplectic” over an investigation the Amazon founder had launched into Pecker’s companies.

“Rather than capitulate to extortion and blackmail, I’ve decided to publish exactly what they sent me, despite the personal cost and embarrassment they threaten,” Bezos, who also owns the Washington Post, wrote.

In the alleged letter to Bezos, Howard wrote that the paper had obtained a “d*ck pick” (sic) of Bezos, as well as text messages and nine other images of Bezos and Lauren Sanchez, with whom he was having an affair. Bezos also published multiple emails, allegedly from AMI representatives, asking the Amazon CEO to release a public statement asserting that AMI’s reporting is not politically motivated.

“Of course I don’t want personal photos published, but I also won’t participate in their well-known practice of blackmail, political favors, political attacks, and corruption,” he continued. “I prefer to stand up, roll this log over, and see what crawls out.”

Bezos’ shocking allegations come one month after the Amazon CEO and his wife, MacKenzie Bezos, announced their divorce. The couple made the announcement shortly before the Enquirer published a story revealing that Bezos was having an affair with Sanchez, a former TV anchor.

After his affair was made public, Bezos said he hired an investigator, Gavin de Becker, to look into how the paper obtained personal text messages included in the story and “to determine the motives for the many unusual actions taken by the Enquirer.”

Bezos also noted in the blog that, as the owner of The Washington Post, he can be a target for Trump and other “powerful people” who are angered over the paper’s reporting.

“It’s unavoidable that certain powerful people who experience Washington Post news coverage will wrongly conclude I am their enemy,” Bezos wrote. “President Trump is one of those people, obvious by his many tweets.”

In an interview with the Post published Tuesday, de Becker, Bezos’ investigator, suggested that Sanchez’s brother, a Trump supporter, may have leaked text messages between Bezos and Sanchez to the Enquirer as a “politically motivated” ploy to embarrass Bezos.

Michael Sanchez denied de Becker’s accusation in a statement to the Post.

According to Howard’s alleged email to Bezos’ team, the photos obtained by the Enquirer showed Sanchez simulating an oral sex scene and Bezos taking a naked selfie in a bathroom.

“Nothing I might write here could tell the National Enquirer story as eloquently as their own words [in the email exchanges],” Bezos wrote in his blog post. “These communications cement AMI’s long-earned reputation for weaponizing journalistic privileges, hiding behind important protections, and ignoring the tenets and purpose of true journalism.”

AMI issued a statement Friday morning saying it launched an investigation into Bezos’ claims, though the company believes it “acted lawfully.”

“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,” the statement said. “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.”

This article has been updated with more details on Bezos’ relationship with Sanchez and accusations against her brother, as well as a statement from AMI responding to Bezos’ claims.