Mark Zuckerberg slammed Apple's controversial App Store policies, the latest in his battle with Tim Cook. Here's where their feud began and everything that's happened since.

In September 2014, Cook gave an in-depth interview with Charlie Rose that touched on a range of topics, including privacy.

During the interview — which took place in the weeks following the infamous leaks of multiple female celebrities' nude photos stored on their iCloud accounts — Cook espoused Apple's commitment to privacy while denouncing the business models of companies like Google and Facebook.

"I think everyone has to ask, how do companies make their money? Follow the money," Cook said. "And if they're making money mainly by collecting gobs of personal data, I think you have a right to be worried. And you should really understand what's happening to that data."

Shortly after, Cook reiterated his stance in an open letter on Apple's dedicated privacy site.

"A few years ago, users of Internet services began to realize that when an online service is free, you're not the customer. You're the product," Cook wrote.

In an interview with Time later that year, Zuckerberg was reportedly visibly irritated by Cook's assertions.

"A frustration I have is that a lot of people increasingly seem to equate an advertising business model with somehow being out of alignment with your customers," Zuckerberg told Time's Lev Grossman. "I think it's the most ridiculous concept. What, you think because you're paying Apple that you're somehow in alignment with them? If you were in alignment with them, then they'd make their products a lot cheaper!"

In 2018, a whistleblower revealed that consulting firm Cambridge Analytica harvested user data without consent from 50 million users.

During an interview with Recode's Kara Swisher and MSNBC's Chris Hayes in the months following, Cook was asked what he would do if he was in Zuckerberg's shoes

Cook responded: "What would I do? I wouldn't be in this situation."

Cook said that Facebook should have regulated itself when it came to user data, but that "I think we're beyond that here." He also doubled down on his stance that Facebook considers its users its product.

"The truth is, we could make a ton of money if we monetized our customer — if our customer was our product," Cook said. "We've elected not to do that."

"You know, I find that argument, that if you're not paying that somehow we can't care about you, to be extremely glib. And not at all aligned with the truth," Zuckerberg said during an interview on The Ezra Klein Show podcast.

He refuted the idea that Facebook isn't focused on serving people and once again criticized the premium Apple places on its products.

"I think it's important that we don't all get Stockholm Syndrome and let the companies that work hard to charge you more convince you that they actually care more about you," he said. "Because that sounds ridiculous to me."

In November 2018, The New York Times published a blockbuster report detailing the fallout from the Cambridge Analytica scandal. The Times reported that Cook's comments had "infuriated" Zuckerberg, who ordered employees on his management team who used iPhones to switch to Android.

Soon after the report published, Facebook wrote a blog post refuting some of the reporting by The Times — but not the Zuckerberg-Cook feud.

"Tim Cook has consistently criticized our business model and Mark has been equally clear he disagrees. So there's been no need to employ anyone else to do this for us," Facebook wrote. "And we've long encouraged our employees and executives to use Android because it is the most popular operating system in the world."

During a company-wide meeting, Zuckerberg openly criticized Apple, saying it has a "unique stranglehold as a gatekeeper on what gets on phones," according to a report from BuzzFeed News.

Zuckerberg also said that the App Store blocks innovation and competition and "allows Apple to charge monopoly rents," BuzzFeed reported.

Apple has been facing antitrust scrutiny from Congress and has been strongly criticized by developers — most notably "Fortnite" creator Epic Games — for the 30% fee it takes from App Store purchases. Apple recently blocked an update to Facebook's iOS app that would have informed users about the fee Apple charges.