Facebook Inc. (FB.O) just lost its most senior product executive. His departure marks the end of an era for the news feed, the social network’s most iconic -- and often most fraught -- product.

Chris Cox, chief product officer at Facebook, worked at the social network for 13 years. He helped invent and develop the news feed, the main channel for personalized life updates for more than 2 billion people -- essentially the algorithm-based editor-in-chief of users’ digital lives. It’s probably no coincidence that Cox’s departure comes just days after Chief Executive Officer Mark Zuckerberg proclaimed that Facebook’s future will be focused on something entirely different: private messaging and small-group chats.

The news feed has been the most important facet of the Facebook business model, because the company can slot advertisements in between personal posts. It’s also been at the center of the company’s controversies, including the spread of false information, because it gives everyone who uses it a different picture of reality. Facebook’s track record of disastrous privacy scandals started when news feed was launched in 2006. Users were outraged to see their posts and photos unexpectedly spilled into an open forum, instead of just on their personal pages. Still, they quickly became addicted.

Now, growth and user engagement have been decelerating in the company’s most important advertising markets. While that hasn’t hurt revenue yet, Facebook has signaled that the slowdown will persist, and that the company will have to spend more money to develop new businesses. As it navigates this transition, Facebook plans to stop telling investors the user numbers for its main social-networking platform alone, choosing instead to disclose an aggregate number of users for Facebook and its WhatsApp, Instagram and Messenger apps. The takeaway from all these changes: News feed has become a legacy product.

The future of Facebook’s business will depend more on ephemeral posts, like those in Instagram Stories, Zuckerberg has said. That shift will also require Facebook to invest more in its messaging products, focusing on encryption -- chats so private not even Facebook can see what people are writing.

That represents a very different social-media universe than the one Cox helped create. In his post about leaving Facebook, he said stewards of social-media products should “take up the daily work of bending it towards the positive, and towards the good. This is our greatest responsibility.”

That won’t be possible in a world dominated by encrypted messaging. Zuckerberg has acknowledged that although private messaging will help Facebook establish trust with users over how their data is handled, in some cases it will be impossible to track some of the most problematic content zipping between the users of his products.

“This will be a big project and we will need leaders who are excited to see the new direction through,” Cox said in his parting post.

His departure was just one piece of a dismal week for the Menlo Park, California-based company. A U.S. criminal probe into Facebook’s data-sharing practices has escalated to include a grand jury, a person familiar with the matter said, a potentially more serious development in the ongoing series of government inquiries to crop up since last March, when reports first surfaced that political consulting firm Cambridge Analytica improperly retained the personal data of millions of Facebook users.

Facebook also weathered its largest-ever service outage, with its social network and other properties like Instagram, WhatsApp and even its Oculus virtual-reality platform going offline around the world starting midday Wednesday. The company blamed a change in its server setup, and said it was considering giving refunds to advertisers.

And U.S. Senator Elizabeth Warren, who is seeking the 2020 Democratic nomination for president, late last week unveiled a plan to break up Facebook and other technology giants like Google and Amazon.com Inc., saying they have outsize power that undermines competition and hurts innovation.