Fidji Simo, who has worked on Facebook's video startegy, will be in charge of the Facebook app, but won't have the VP of Product title Cox did.
Neither Cox nor Zuckerberg specified what led to their split. He had left a graduate program at Stanford University to join Facebook in 2005 as a software engineer and helped developed its original news feed feature.
Cox and Zuckerberg appear to be divided over the company's new strategy announced last week that it would focus on privacy rather than connecting with the world at large. Both men are long-serving Facebook veterans - Cox was one of Facebook's earliest employees, and Daniels has been with the company since 2011 - and trusted lieutenants of Mark Zuckerberg.
Cox's unexpected departure, which he and Zuckerberg announced in separate Facebook posts Thursday, comes months after Cox was promoted in a major reorganization. The leaders of each of Facebook's main products (Facebook, Instagram, Messenger, and WhatsApp) will now report directly to Zuckerberg. He also built Facebook's first human resources teams and oversaw the strategy for the apps that Facebook owns, Zuckerberg wrote.
Daniels, meanwhile, headed up WhatsApp since co-founder Jan Koum's departure in April. This is an important change as we begin the next chapter of our work building the privacy-focused social foundation for the future.
Chris Daniels, who took charge of WhatsApp after the founders' departure previous year, is also leaving the company.
SUNDAY ALAMBA APFacebook's Chief of Product officer Chris Cox was long one of CEO Mark Zuckerberg's top deputies
The departures of Cox and Daniels come a day after a technical issue that limited use of Facebook and Instagram for most of Wednesday.
"This will be a big project and we will need leaders who are excited to see the new direction through", he wrote, signaling that he wasn't "excited" about it himself.
Daniels has been at Facebook almost nine years, and previously led the company's Internet.org effort, a project aimed at bringing internet access to developing countries.
Cox gained greater oversight of WhatsApp and Instagram following the exits of their founders over the last two years.
Zuckerberg said on Thursday that Olivan will now lead the effort to integrate Facebook apps, a key move as the company encrypts conversations on more of its messaging services and makes them compatible.
Hundreds of South Florida passengers affected by grounding of Boeing aircraft
American President Donald Trump on Wednesday said the United States would ground all Boeing 737 Max 8 and Max 9 planes "effective immediately".