Facebook head Mark Zuckerberg has announced the resignation of the company’s Chief Product Officer, Chris Cox, and the head of WhatsApp, Chris Daniels.

Cox has been with Facebook for more than a decade and currently oversees the company’s core suite of apps. The heads of all of Facebook’s most important teams — Instagram, WhatsApp, Messenger, and Facebook itself — all report to him. He’d been floated as the next CEO, should Zuckerberg ever step away.

Daniels took over WhatsApp last May after WhatsApp co-founder Jan Koum left. Prior to that, he’d been running Facebook’s internet.org initiative, which was meant to bring internet regions of the world currently without connectivity. Under his leadership, WhatsApp added forwarding limits to decrease the spread of misinformation. It also announced plans to being showing advertisements, despite being founded on a promise of never showing ads.

Facebook doesn’t plan to appoint anyone to immediately fill Cox’s role. Zuckerberg announced that Will Cathcart will be the new head of WhatsApp and Fidji Simo will be the new head of the Facebook app.

“This is an important change as we begin the next chapter of our work building the privacy-focused social foundation for the future,” Zuckerberg said in a note.

Facebook has lost several top executives during the last two years, including its general counsel, chief security officer, and co-founders of WhatsApp, Instagram and Oculus, a virtual reality firm it bought in 2014.