WhatsApp co-founder Jan Koum is leaving Facebook and is expected to step down from the board

WhatsApp co-founder Jan Koum is leaving Facebook, the company that acquired his messaging startup and made him a billionaire, to take “time off to do things I enjoy outside of technology, such as collecting rare air-cooled Porsches, working on my cars and playing ultimate frisbee,” he wrote on his Facebook page Monday.

Koum is also a member of Facebook’s board of directors and is expected to step down, according to people Recode spoke to. When Facebook filed its annual proxy statement earlier this month, it listed Koum as up for re-election at the company’s annual shareholder meeting.

The Washington Post first broke the news. A company spokesperson pointed Recode to Koum’s post and declined to comment on his board seat.

Koum has been with Facebook since February of 2014, when Facebook acquired the messaging startup for $16 billion. (The deal was worth even more by the time it closed.) In that time, WhatsApp has grown into one of the world’s most dominant messaging platforms, with more than 1.2 billion users worldwide. It’s particularly important in countries where wireless internet is not as reliable, like India and Brazil.

But Koum and WhatsApp were always a little outside of the Facebook norm. Despite sitting on the board, Koum was rarely a public face for WhatsApp or Facebook. He and co-founder Brian Acton were extremely private — WhatsApp’s office used to be separate from Facebook’s, without any signage — and were huge believers in security tools like encrypted messaging. Before the acquisition, WhatsApp promised it would never run ads. It was a promise the company was going to have a hard time keeping with WhatsApp under Facebook’s control.

Those close to Koum felt like his departure was always a possibility, especially after fellow co-founder Brian Acton left in September. (Acton caused a stir last month when he tweeted out that everyone should #DeleteFacebook.) The Washington Post reported that Koum’s departure is in part because he was “clashing with its parent, Facebook, over the popular messaging service’s strategy and Facebook’s attempts to use its personal data and weaken its encryption.”

Facebook CEO Mark Zuckerberg replied to Koum’s farewell post, citing encryption as one of the things he learned a lot about from Koum.

“I’m grateful for everything you’d 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.”

Koum’s departure is one of the few high profile departures to date — the company’s exec team is very loyal and most have been there close to a decade or more. Earlier this year, it was learned that Chief Security Officer Alex Stamos is also planning to leave the company after some clashes with higher-ups.

Facebook’s big developer conference, F8, kicks off tomorrow morning in San Jose.

This article originally appeared on Recode.net.