The co-founders of photo-sharing giant Instagram, Kevin Systrom and Mike Krieger, are both leaving the firm.
Mr Systrom, chief executive, said they were departing to “explore our curiosity and creativity again”.
Instagram, purchased by Facebook in 2012 for $1bn (£760m) in cash and stock, has more than a billion users.
There had been reports of tension between the pair and Facebook, and the departures add to what has been a troubling year for the parent company.
Mr Systrom, 34, the CEO, and Mr Krieger, 32, the chief technical officer, started the image sharing site in 2010 and continued to run the service after it was acquired by Facebook.
What have the pair said?
Not a great deal. They reportedly only told the Facebook leadership on Monday so the departure appears pretty sudden.
In a blog post, Mr Systrom said: “We’re now ready for our next chapter.”
He added: “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.”
There was no animosity in the blog post. Mr Systrom said the pair both remained “excited for the future of Instagram and Facebook”.
How has Facebook responded?
CEO Mark Zuckerberg said in a statement that Instagram reflected the founders’ “combined creative talents”.
“I’ve learned a lot working with them for the past six years and have really enjoyed it,” he said. “I’m looking forward to seeing what they build next.”
So what’s behind the departures?
The BBC understands that tension started to grow between Mr Systrom and Mr Zuckerberg as far back as 2014 when Facebook purchased WhatsApp.
The social network spent $19bn on the chat app in 2014, and Instagram’s co-founder is said to have become concerned that he had sold out too soon.
He also saw Snapchat prosper – an app Facebook had tried and failed to take over.
“The irony is that Kevin built the more successful product,” one insider commented.
There are reports that Mr Systrom had sought to maintain Instagram’s independence and that this trickled down to make staff on Facebook and Instagram less inclined to be collaborative.
But there was pressure for their two apps to become more integrated, and features were added allowing, for example, Instagram Stories – videos that self-destruct after 24 hours – to be cross-posted to Facebook.
Despite remaining Instagram’s figurehead at product launches and other public appearances, Mr Systrom’s influence declined over time, a source told the BBC, as more Facebook executives were transferred to the photo service.
“Kevin maybe didn’t have the fight in him anymore and probably didn’t agree with some of the product decisions,” the source said. “This is just the natural end to an era.”