In the wake of a Washington Post report that alleged a "clash" over Facebook data practices, WhatsApp co-founder and Facebook board member Jan Koum confirmed that he is leaving the company, effective immediately.

"It's been almost a decade since Brian and I started WhatsApp, and it's been an amazing journey with some of the best people," Koum posted on his personal Facebook page on Monday. "But it is time for me to move on." His status included a Facebook "emotional" tag indicating that he is "sad."

Koum's post doesn't include an explanation of exactly why he's leaving other than "doing things I enjoy outside of technology." That leaves WaPo's Monday report as the loudest possible explanation available at the moment.

Reporter Elizabeth Dwoskin claims that the move came as a result of Koum's disagreements with "Facebook's attempts to use [WhatsApp]'s personal data and weaken its encryption." The report describes how those issues gradually emerged after Facebook's purchase of the encrypted-messaging platform for $16 billion in 2014 and how they led Koum to inform Facebook's corporate leadership of his impending departure. From the sound of things, these disagreements began taking shape well before the company's Cambridge Analytica scandal.

The issues at stake include Facebook's demand for more user data being attached to WhatsApp profiles—in spite of the app's buyout including promises that it would "remain autonomous and operate independently." Dwoskin reports that, during one change to WhatsApp's terms of service, Facebook bosses wanted to create user-specific profiles that could reach across platforms like Facebook and Instagram—and thus be used "for ad-targeting or for Facebook’s data-mining."

More recently, according to the report, Koum and other WhatsApp staffers struggled with Facebook's desire to make its new WhatsApp For Business product "easier for businesses to use its tools." This would apparently require weakening WhatsApp's existing end-to-end encryption—a feature that the company added to its weak-at-the-time encrypted-messaging services in 2016. (If you're keeping score, that 2016 rollout still had issues, including a lack of notifications when a user's encryption key has changed.)

As Dwoskin points out, WhatsApp's other co-founder, Brian Acton, has been far more vocal of his Facebook disapproval since leaving the company in November. He's done so directly by posting support of a "#DeleteFacebook" movement, and he's indirectly made the point by contributing $50 million to the Signal Foundation, which develops and supports the encrypted-messaging app Signal (arguably WhatsApp's largest competition as of late). And Acton and Koum may be followed by an even larger falloff, as the WaPo report suggests November as a mass-exodus point, when original WhatsApp staffers will be allowed to exercise stock options.

Koum's Monday announcement included a response from Facebook CEO Mark Zuckerberg, timestamped 15 minutes after Koum's post. "I'm grateful for everything you've done to help connect the world and for everything you've taught me, including about encryption and its ability to take power from centralized systems and put it back in people's hands," Zuckerberg wrote. "Those values will always be at the heart of WhatsApp."

When reached for comment, Facebook representatives pointed us to Koum's post.