Facebook’s mobile ambitions clearly aren’t suffering. Over one billion people use Facebook on their mobile devices each month, the social network announced Wednesday, and mobile ads account for almost 60 percent of Facebook’s advertising revenue.

But some of the company’s biggest growth isn’t on Facebook proper, but in private messaging.

More than 200 million people use Facebook Messenger each month, Facebook CEO Mark Zuckerberg said during Wednesday’s first quarter earnings call. This is the first time the social network has released numbers describing just how popular the messaging application is.

Just a day earlier, WhatsApp—the hugely popular messaging app that Facebook acquired earlier this year—announced it hit the 500 million user mark, putting its well on its way to becoming the next billion-user app. 

See also: The Facebook Effect: WhatsApp Is Well On Its Way To A Billion Users

What isn’t clear, though, is how many of those users overlap, or how many of them are messaging-only consumers. 

Zuckerberg added that with Messenger and WhatsApp, the company is moving quickly toward more private messaging, a significant shift from the traditional use for Facebook—connecting with as many “friends” as you possibly can to amass a list of hundreds of acquaintances.

It’s likely the number of Messenger users will continue to climb. The company recently said it’s ripping messaging features out of the Facebook application and forcing all users to download Messenger in order to connect privately. 

Image via Facebook