So what will become of Instagram now?
Systrom and Zuckerberg reportedly clashed multiple times a year although they still got along and were able to resolve disputes. Without revealing any specifics, Systrom said he and Krieger plan to build "things" at some point in the future.
Krieger and Systrom founded Instagram in 2010; Facebook acquired the young photo-sharing platform for a whopping $715 million in 2012.
"Our sense is the duo may have wanted to run Instagram more independently than their parent company wanted", said Scott Kessler, an analyst at the research firm CFRA. And while Facebook's Q2 earnings report showed Facebook's ad revenue growth was slowing, ad spend on Instagram grew four times that of Facebook year over year, according to a Q2 report from Merkle.
He later tweeted, "The @instagram journey is one I won't forget".
The people close to the matter have said that the co-founders didn't provide a reason for stepping down.
However. There have been reports of tension between the founders and Mark Zuckerberg, and their resignations come after a year when we've seen a stream of Facebook scandals.
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These days, Instagram is Facebook's most prized possession, though the ouroboros of Instagram and Facebook is hard to parse.
Facebook bought Instagram in 2012, just before going public, at a price that seemed inconceivable at the time - $1 billion - especially for a little-known startup with no profit. In fact, it's already done this by adding tools like messaging, the ability to mute users and indications showing whether someone is online. Offered through Instagram and as a standalone app, IGTV serves up longer-length video content, mostly from popular Instagram users.
Instagram, meanwhile, has remained a bright spot for the company. In June, at the launch of IGTV, Systrom announced the app had reached 1 billion monthly active users. People still loved it, to a degree that they haven't loved Facebook for years now, if they ever did.
That fuelled investor concern over the sudden loss of the pair, which follows the departures of WhatsApp co-founders Jan Koum and Brian Acton and a reshuffling of Facebook's executive ranks earlier this year.
Instagram Stories have been a hit on the platform.
But the blow to Facebook is far more than optics. COO Sheryl Sandberg also noted ads have "expanded quite nicely" to Instagram, and it represents a "very healthy part" of growth, which is expected to continue.