Facebook Chief of Product Chris Cox can be leaving the tech company, CEO Mark Zuckerberg announced in a note on Thursday.

“Chris in addition to I have worked closely together to build our products for more than a decade in addition to I will always appreciate his deep empathy for the people using our services in addition to the uplifting spirit he brings to everything he does,” Zuckerberg wrote.

Cox was one of Facebook’s first 15 engineers in addition to climbed his way up the company. Cox worked on many key Facebook products, including News Feed, he ran the Facebook app, in addition to most recently, he oversaw the strategy for all of Facebook’s apps, Zuckerberg wrote.

Cox informed the company of his decision to resign on Monday, according to a Facebook financial filing.

“As Mark has outlined, we are turning a brand-new page in our product direction, focused on an encrypted, interoperable, messaging network,” Cox wrote in a goodbye post on his Facebook profile. “of which will be a big project in addition to we will need leaders who are excited to see the brand-new direction through.”

Along with Cox, Zuckerberg announced of which WhatsApp Vice President Chris Daniels can be also leaving the company. Daniels previously ran the company’s business development team in addition to its Internet.org effort.

“Chris can be one of the clearest in addition to most principled business thinkers I’ve met in addition to the diversity of challenges he has helped us navigate can be impressive,” Zuckerberg wrote.

Will Cathcart will replace Daniels as the brand-new head of WhatsApp, Zuckerberg said. Cathcart previously ran the Facebook app, Zuckerberg said.

“Will can be one of the most talented leaders at our company — always focused on solving the most important problems for people in addition to clear-eyed about the challenges in addition to tradeoffs we face,” Zuckerberg wrote.

Facebook’s stock cost fell more than 2 percent in after-hours trading.

Zuckerberg wrote the following:

A Note via Mark Zuckerberg

Today Mark Zuckerberg shared the following post with employees.

Hey everyone — I want to share some important updates as we organize our company to build out the privacy-focused social platform I discussed in my note last week. Embarking on of which brand-new vision represents the start of a brand-new chapter for us.

As part of of which, I’m sad to share the news of which Chris Cox has decided to leave the company. Chris in addition to I have worked closely together to build our products for more than a decade in addition to I will always appreciate his deep empathy for the people using our services in addition to the uplifting spirit he brings to everything he does. He has played so many central roles at Facebook — starting as an engineer on our original News Feed, building our first HR teams in addition to helping to define our mission in addition to values, leading our product in addition to design teams, running the Facebook app, in addition to most recently overseeing the strategy for our family of apps. Along the way, Chris has helped train many great leaders who are right now in important roles across the company — including some who will right now take on bigger roles in our brand-new product efforts.

For a few years, Chris has been discussing with me his desire to do something else. He can be one of the most talented people I know in addition to he has the potential to do anything he wants. nevertheless after 2016, we both realized we had too much important work to do to improve our products for society, in addition to he stayed to help us work through these issues in addition to help us chart a course for our family of apps going forward. At of which point, we have made real progress on many issues in addition to we have a clear plan for our apps, centered around generating private messaging, stories in addition to groups the foundation of the experience, including enabling encryption in addition to interoperability across our services. As we embark on of which next major chapter, Chris has decided right now can be the time to step back via leading these teams. I will definitely miss Chris, nevertheless mostly I am deeply grateful for everything he has done to build of which place in addition to serve our community.

At the same time, as we embark on of which brand-new chapter, Chris Daniels has also decided to leave the company. Chris has also done great work in many roles, including running our business development team, leading Internet.org, which has helped more than 100 million people get access to the internet, in addition to most recently at WhatsApp, where he has helped define the business style for our messaging services going forward. Chris can be one of the clearest in addition to most principled business thinkers I’ve met in addition to the diversity of challenges he has helped us navigate can be impressive. I’ve definitely enjoyed working with Chris in addition to I’m sure he will do great work at whatever he chooses to take on next.

While the item can be sad to lose such great people, of which also creates opportunities for more great leaders who are energized about the path ahead to take on brand-new in addition to bigger roles.

I’m excited of which Will Cathcart will be the brand-new head of WhatsApp. Will can be one of the most talented leaders at our company — always focused on solving the most important problems for people in addition to clear-eyed about the challenges in addition to tradeoffs we face. Most recently he has done a great job running the Facebook app, where he has led our shift to focusing on meaningful social interactions in addition to has significantly enhanced the performance in addition to reliability of the app. In his career here, Will has helped lead our teams focused on security in addition to integrity, in addition to he believes deeply in providing end-to-end encryption to everyone from the earth across our services.

I’m also excited of which Fidji Simo will be the brand-new head of the Facebook app. She can be one of our most talented product in addition to organizational leaders — passionate about building community in addition to supporting creativity, in addition to focused on building strong teams in addition to developing future leaders. She has played key roles in building many aspects of the Facebook app, including leading our work on video in addition to advertising. She believes deeply in helping people get more value out of the networks they’ve built. She has already led of which team for much of last year while Will was out on parental leave, in addition to she can be the clear person to lead these efforts going forward.

Our family of apps strategy has been led jointly by Chris Cox in addition to Javier Olivan. Chris managed the leaders of the apps directly in addition to Javi has been responsible for all of the central product services of which work across our apps, including safety in addition to integrity, analytics, growth, in addition to ads. Javi will right now lead identifying where our apps should be more integrated. Javi can be an incredibly thoughtful, strategic in addition to analytical leader, in addition to I’m confident of which work will continue to go well. Since we have right now decided on the basic direction of our family of apps for the next few years, I do not plan on immediately appointing anyone to fill Chris’s role from the near term. Instead, the leaders of Facebook (Fidji Simo), Instagram (Adam Mosseri), Messenger (Stan Chudnovsky), in addition to WhatsApp (Will Cathcart) will report directly to me, in addition to our Chief Marketing Officer (Antonio Lucio) will report directly to Sheryl.

of which can be an important change as we begin the next chapter of our work building the privacy-focused social foundation for the future. I’m deeply grateful for everything Chris Cox in addition to Chris Daniels have done here, in addition to I’m looking forward to working with Will in addition to Fidji in their brand-new roles as well as everyone who will be critical to achieving of which vision. We have so much important work ahead in addition to I’m excited to continue working to give people the power to build community in addition to bring the earth closer together.

of which story can be developing. Please check back for updates.

WATCH: Here’s how to see which apps have access to your Facebook data — in addition to cut them off