Six years after selling Instagram to Facebook, co-founders Kevin Systrom and Mike Krieger have announced their resignation. Having been deeply involved in the running of the company since its inception eight years ago, their departure is greatly unexpected.

Systrom said in an official statement:

Mike and I are grateful for the last eight years at Instagram and six years with the Facebook team. 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 one billion. We’re now ready for our next chapter.

We’re planning on taking some time off to explore our curiosity and creativity again. 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.

Though the statement doesn’t give a reason for the co-founders’ departure, according to TechCrunch, anonymous sources state that it was a result of conflict regarding Instagram’s autonomy. When Instagram’s VP of Product Kevin Weil moved to Facebook’s new blockchain team in May, he was replaced by a member of Mark Zuckerburg’s inner circle, VP of Facebook News Feed Adam Mosseri. Mosseri and Systrom reportedly did not get along well, and the issue was exacerbated by other departures, and disagreements between Zuckerberg and Systrom about integrations between the apps.

Will their resignation have a large negative impact for Facebook? As Facebook use continues to decline among the youngest demographic, Instagram is currently Facebook’s most successful acquisition, giving them a chance to compete against Snapchat. It will be interesting to see who will lead the company in their wake, and if they will be able to continue Instagram’s success.