Instagram founders Kevin Systrom and Mike Krieger resigned from the company Monday. They said they want to "take some time off to explore their creativity again."

“Mike and I are grateful for the last eight years at Instagram and six years with the Facebook team. We have grown from 13 people to over a thousand with offices all around the world, all while building products used and loved by a community of over one billion. We are now ready for our next chapter,” Systrom said in a statement Monday night.

The New York Times reported that Systrom, Instagram’s chief executive officer, and Krieger, the chief technical officer, notified the video-sharing giant’s leadership team and Facebook of their decision Monday. The two didn't give a reason for their departure but said they were planning to take time off after leaving the company.

However, according to latest reports, the duo decided to leave after increasing tension with Facebook CEO Mark Zuckerberg over the direction of the company.

“We are 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,” Systrom said.

Zuckerberg responded to their departure saying, “Kevin and Mike are extraordinary product leaders and Instagram reflects their combined creative talents. I have learned a lot working with them for the past six years and have really enjoyed it. I wish them all the best and I am looking forward to see what they build next.”

The duo founded the photo-sharing app in 2010. Facebook acquired the company in 2012 for $1 billion. The company has since grown to a community of more than 1 billion monthly users, thus making it Facebook’s most successful acquisition.

“When Instagram joined us, the team had only 16 people. We believe Instagram has been able to use Facebook’s infrastructure to grow more than twice as quickly as it would have on its own. A big congratulations to the Instagram team — and to all the teams across our company that have contributed to this success,” Zuckerberg said on the company’s Q2 earnings call July 25, 2018.

Systrom remained the CEO of Instagram despite the acquisition. Though Systrom’s app failed to earn him the same level of wealth as Zuckerberg, he is currently worth $1.67 billion, Business Report reported.  The acquisition in 2012 gave him a net worth of $400 million. Two years later the value of Systrom's Facebook stock doubled, leaving him with a net worth of $800 million. Krieger, on the other hand, is worth $500 million as of 2017.

“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. We look forward to watching what these innovative and extraordinary companies do next,” Systrom said Monday.

Their exit raises questions about the company’s future at a time when Facebook faces its most sustained set of crises in its history.