Kevin Systrom and Mike Krieger, who co-founded Instagram in 2010 and sold the app to Facebook two years later for $1 billion, announced in a blog post that they would be leaving the company. The two men were responsible for shaping the culture and products of Instagram — Systrom serving as CEO and product visionary, and CTO Krieger actively running the engineering team. They built the company to over a thousand employees and the user community to more than one billion. “We’re planning on taking some time off to explore our curiosity and creativity again,” wrote Systrom. “Building new things requires that we step back, understand what inspires us and match that with what the world needs; that’s what we plan to do.”

According to sources, Systrom and Krieger are resigning their positions at the photo- and video-sharing service due to their frustration with Facebook CEO Mark Zuckerberg’s increasing control over the company. They plan to leave in the coming weeks.

“The co-founders have disagreed with Zuckerberg on a handful of recent product changes, including changes to comments and how posts are shared between the two networks,” reports Recode. “The departures are a major blow to Facebook. Instagram, which has grown rapidly and is popular with the younger generation of users who are less interested in Facebook, has been a consistent beacon of good news for a company that has had more than a year of bad news.”

The departures “create uncertainty around the app,” suggests The New York Times. “It is unclear who will lead the company on the founders’ departures, and if that person can continue Instagram’s longstanding success streak.”

Zuckerberg wished Systrom and Krieger “all the best” and said he is “looking forward to seeing what they build next.”

WhatsApp founder and CEO Jan Koum also departed earlier this year over reported disagreements with Facebook management.