The co-founder of WhatsApp - the messaging app that Facebook bought for $19 billion in 2014, its largest-ever acquisition - is leaving the company, CNBC reports.
Jan Koum said in a Facebook post on Monday that it was time to "move on" and take time to do things outside of technology.
"And I'll still be cheering WhatsApp on – just from the outside," he wrote.
The Washington Post, which earlier reported details of Koum's departure, said Koum would leave both WhatsApp and Facebook's board. Facebook did not address Koum's future role at Facebook when contacted by CNBC.
Koum's departure comes at a crucial time at Facebook as the company reels from revelations of Russian election manipulation, fake news, data leaks and more. Koum has long been an advocate of privacy, writing in 2014 about his experience growing up in the USSR when he feared communications would be monitored by the KGB. In 2012 he posted a salvo about Google's data collection, writing, "Your data isn't even in the picture. We are simply not interested in any of it."
Koum's Monday post announcing his departure did not mention privacy concerns, and did not specifically address his roles in Facebook outside WhatsApp. But according to the Post, Koum was "worn down by the differences in approach," particularly around data targeting, encryption, ad-based revenue and mobile payments.
Facebook CEO Mark Zuckerberg responded to the post on Monday, writing he was thankful for what Koum taught him about "about encryption and its ability to take power from centralized systems and put it back in people's hands."
"Those values will always be at the heart of WhatsApp," Zuckerberg wrote in a comment on Koum's Facebook post. But Zuckerberg has also pushed WhatsApp to "move faster" to grow its business base, despite scrutiny from the European Commission surrounding the company.