A security consultant working for Jeff Bezos says the Saudi government somehow gained access to the Amazon boss's mobile phone.
The probe followed the publication by the National Enquirer tabloid of details of Bezos' extramarital affair, including intimate texts and photos.
Bezos, who also owns the Washington Post, has long alleged that Saudi Arabia may have played a role in the incident as revenge for the Post's coverage of the murder of journalist Jamal Khashoggi at the Saudi Consulate in Istanbul.
Saudi Arabia has always flatly denied any involvement in the dispute and Reuters cannot independently verify the claims made by Gavin De Becker, who has known Bezos for two decades.
This is the first time that an official connected to Bezos has so bluntly stated that the Saudis played a direct role in cyber espionage against him, though.
It's not made clear how they would have gained access.
Writing in the Daily Beast, De Becker says he cannot divulge specific evidence due to ongoing federal investigations.
But he says he's not sure what the National Enquirer's parent company, AMI, may have known of the details.
De Becker also alleges AMI tried to force him and Bezos to sign agreements denying the company played any role in, quote, "electronic eavesdropping or hacking in their news-gathering process." Jeff Bezos claimed AMI tried to blackmail him when he first went public with the incident in February.
AMI has said all of its reporting on Bezos was done legally.
The Saudi embassy in Washington has not returned a request for comment.