It's currently a free platform enjoyed by nearly two billion people.
But users can expect a significant change in their experience of WhatsApp, next year – when Facebook bosses plan to flood it with adverts.
The Android and iOS chat app, which was originally released in 2009, will start to embed paid-for content in the app's Status feature from 2019.
It comes five years after Mark Zuckerberg's company bought the platform from co-founders Jan Koum and Brian Acton for a whopping £22billion.
Both Koum and Acton later quit Facebook, citing differences with the social media company.
Insiders believe they were unhappy that their beloved product - which was originally marketed as advert-free and end-to-end encrypted - would soon host commercial content at the expense of users' privacy.
Specifically, although the latter will remain unchanged, the men were unhappy that Facebook wanted to share data across platforms in order to customise the adverts.
Venting his frustration, Acton took to Twitter in March where he posted: 'It is time. #deletefacebook.'
He hasn't posted anything since, but later told Forbes magazine: 'Targeted advertising is what makes me unhappy.
'You build it [the platform] once, it runs everywhere in every country. You don’t need a sophisticated sales force. It’s a very simple business.'
Adding his opinion on the Facebook team, he said: 'They represent a set of business practices, principles and ethics, and policies that I don’t necessarily agree with.'
These were echoed by his former co-founder Koum in 2012. Writing in a blog post, he said:
'These days companies know literally everything about you, your friends, your interests, and they use it all to sell ads.
'At every company that sells ads, a significant portion of their engineering team spends they day tuning data mining, writing better code to collect your personal data.
'Remember, when advertising is involved, you the user are the product.'
However, last month, Facebook's chief security officer, Alex Stamos, justified the planned changes, claiming that it was unrealistic for people to expect it to remain free forever - even though that was the original vision.
He wrote: 'It is foolish to expect that FB shareholders are going to subsidise a free text/voice/video global communications network forever.
'Eventually, WhatsApp is going to need to generate revenue.
'This could come from directly charging for the service, it could come from advertising...'