By June of this year, that number reached 1 billion. Despite the sale, they remained at the helm of the photo-sharing site.
Facebook can't afford to let that growth stall.
Systrom's fortune is valued at $1.4 billion by Forbes.
All of this said, hopefully Kevin and Mike's departure doesn't foreshadow an increasing Facebookification of Instagram.
The departures are a challenge for Facebook. After the break, they plan to build something new.
Facebook doesn't break out Instagram's revenue, but it has frequently called out the app in earnings calls.
"Instagram has more heavy usage of Stories, so that's an area of continued growth opportunity because the effective levels of monetization in Stories are lower", Mr. Wehner said.
The photo app's global revenue this year is likely to exceed $8 billion, showed data from advertising consultancy EMarketer.
Airplane passengers reportedly bleed from noses during flight
As a result, the aircraft had to fly back to an airport to give treatment to those affected on the plane carrying 166 passengers. This led to an imbalance in the cabin pressure and oxygen masks were deployed with which most passengers breathed.
In an interview with The Wall Street Journal that was conducted before Monday's announcement, Kevin makes clear he has no regrets about having sold Instagram to Facebook back in 2012.
"Those are signs that [Zuckerberg] definitely wants more Facebook influence on Instagram", Williamson said. Yes, lovely photos on Instagram can still make people feel bad, and Instagram can still be manipulated by propagandists or used to bully people.
One sign that additional integration may be in Instagram's future: Zuckerberg in May sent longtime Facebook executive Adam Mosseri to run Instagram's product operation.
It comes after months of chaos and scandals for Facebook.
Worst of all: Will it just become another Facebook?
"In a sense, Facebook, which was once itself an upstart, has now become the establishment", said Stephen Allan, world-wide chairman and CEO of Mediacom, a media agency owned by ad giant WPP PLC.
The optics are awful, first off. Facebook is trying to project confidence that it's moving past its two years of near constant crises involving foreign propaganda infecting the social network, of people and government officials using Facebook and its WhatsApp app to incite violence, and realisations stemming from this year's Cambridge Analytica scandal that Facebook may not be worthy of people's trust with their private time and digital lives.
Tied with this, Instagram is also increasingly popular with brands, who benefit from Facebook's sophisticated targeting capabilities and the popularity of Instagram with a hard-to-reach younger demographic.
Mark Douglas, CEO of the ad tech company Steelhouse, agrees that Systrom's and Krieger's departures will have zero impact on Instagram's ad business.