Instagram co-founders Kevin Systrom and Mike Krieger resigned from the photo-sharing company today. The news was first reported by The New York Times and confirmed in a blog post written by Systrom. Sources speaking to Bloomberg say Systrom and Krieger were frustrated by an uptick in Facebook CEO Mark Zuckerberg’s meddling, as Facebook became increasingly reliant on Instagram for its future.

“We’re planning on taking some time off to explore our curiosity and creativity again,” Systrom wrote in the blog post. “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.”

Valued at many times the $1 billion that Facebook CEO Mark Zuckerberg agreed to purchase it for and now counting more than 1 billion worldwide users, Instagram is arguably Facebook’s most successful acquisition. Its growth since 2012 is largely a product of Systrom and Krieger’s vision, the duo’s strategic use of Facebook resources, and the willingness to aggressively compete with Snapchat. “Mike and I are grateful for the last eight years at Instagram and six years with the Facebook team,” Systrom wrote. “We’ve grown from 13 people to over a thousand with offices around the world, all while building products used and loved by a community of over 1 billion.”

Systrom and Krieger built Instagram to 1 billion users and helped Facebook thwart Snapchat

“Kevin and Mike are extraordinary product leaders and Instagram reflects their combined creative talents,” said Mark Zuckerberg in a statement. “I’ve learned a lot working with them for the past six years and have really enjoyed it. I wish them all the best and I’m looking forward to seeing what they build next.”

Now, Systrom and Krieger’s exit may impact the social network’s ability to manage its ongoing crises around election interference, fake news, and a general public perception that Facebook is no longer healthy for society or democracy. Instagram has been positioned as a fast-growing and successful alternative to Facebook for teenage users and those disillusioned by Facebook’s privacy violations and its larger impact on digital life. Without Systrom and Krieger at the helm, Instagram may struggle to continue growing at its previous pace while also maintaining independence from the Facebook juggernaut.

Systrom and Krieger represent the second pair of wildly successful co-founders to sell a company to Facebook for billions and then depart some years later. Earlier this year, WhatsApp co-founder Jan Koum announced he was leaving Facebook over apparent disagreements about user privacy and data-sharing. Koum’s fellow co-founder Brian Acton left Facebook in September 2017, and Acton has voiced not-so-subtle criticisms of his former employer on Twitter and through his investment of encrypted messaging company Signal. If Systrom or Krieger share similar misgivings about Facebook as Koum and Acton, they’re not letting on — publicly, at least.

“We remain excited for the future of Instagram and Facebook in the coming years as we transition from leaders to two users in a billion,” Systrom wrote. “We look forward to watching what these innovative and extraordinary companies do next.”

Update September 24th 11:05PM ET: This story has been updated to reflect confirmation from Instagram CEO Kevin Systrom that he and Mike Krieger are leaving the company.