Amazon.com Inc. founder Jeff Bezos and his allies have publicly speculated about how the National Enquirer acquired racy texts he sent to his girlfriend, including at one point hinting Saudi Arabia or the White House may have been involved.

The reality is simpler: Michael Sanchez, the brother of Mr. Bezos’ lover, sold the billionaire’s secrets for $200,000 to the Enquirer’s publisher, said people familiar with the matter.

The...