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WhatsApp co-founder Brian Acton became a multibillionaire when Facebook bought his messaging app in 2014 for an eye-popping $22 billion. But it's a decision that seems to unsettle him, according to a profile of Acton published by Forbes on Wednesday.

Acton left WhatsApp in 2017, and CEO Jan Koum followed in August. Acton's exit, which occurred before his Facebook stock fully vested, cost him $850 million, according to Forbes.

The major divide with Facebook was reportedly over monetizing the messaging app, which has 1.5 billion users. Koum and Acton had been resistant to adopting Facebook's widely lucrative targeted advertising model, which uses personal data to let marketers show ads to specific types of users on the social network. The disagreements led to tensions with Facebook CEO Mark Zuckerberg and COO Sheryl Sandberg.

"I sold my users' privacy to a larger benefit," Acton told Forbes. "I made a choice and a compromise. And I live with that every day."

Facebook didn't immediately respond to a request for comment.

The social network has been under intense scrutiny since its Cambridge Analytica scandal in March, which revealed that 87 million Facebook users had their personal information harvested by a UK-based digital consultancy. At the time, Acton tweeted, "It is time. #deletefacebook."

Acton's comments on Wednesday come as Facebook deals with the exits this week of Instagram co-founders Kevin Systrom and Mike Krieger. Their departures were also reportedly due to clashes with Zuckerberg, who's said to have tightened his grasp on Instagram in recent months.

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Late Wednesday, David Marcus, head of Facebook's blockchain division, shot back against Acton in a Facebook post. "I find attacking the people and company that made you a billionaire, and went to an unprecedented extent to shield and accommodate you for years, low-class," he wrote. "It's actually a whole new standard of low-class."

First published September 26, 11:07 a.m. PT.

Updated, 2:52 p.m. PT: Adds statement from Facebook's David Marcus.

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