WhatsApp founders Jan Koum and Brian Acton reportedly left $1.3 billion behind by leaving Facebook.

According to The Wall Street Journal, both men chose to depart after a number of long-standing disputes. 

The major divide was over monetizing the messaging app, which has 1.5 billion users. Koum and Acton had been resistant in 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 between Facebook CEO Mark Zuckerberg and COO Sheryl Sandberg, according to the report. 

The troubles between WhatsApp and Facebook also included culture clashes. WhatsApp employees preferred a quieter work environment -- the opposite of Facebook's bustling and sprawling Silicon Valley campus. There was also resentment over WhatsApps larger desks and requests for nice bathrooms, the Journal report said. 

Acton departed Facebook first in November 2017, and in doing so he forfeited $900 million in potential stock rewards, the WSJ reports, citing people it describes as familiar with what happened. Koum's departure, announced in April and effective as of August, means he will leave behind 2 million unvested Facebook shares worth $400 million.

Had Koum and Acton stayed at the company until November, they would have received all of those shares upon the completion of their contracts.

Koum's announcement came amid Facebook's Cambridge Analytica data scandal. The UK-based political consultancy, which had ties to the Trump presidential campaign, had improperly accessed personal information on up to 87 million Facebook users. The controversy triggered a backlash over Facebook's data collection policies and raised broader questions about Facebook's targeted advertising model. 

The WSJ report tells a longer story of the WhatsApp founders' breakup with Facebook, including the two men's efforts to minimize advertising within the app and the company's reported reaction to Acton tweeting "It is time. #delete Facebook" when the Cambridge Analytica scandal began.

Facebook did not immediately respond to CNET's request for comment.

Update, 10:48 a.m. PT: Adds more background.

Cambridge Analytica: Everything you need to know about Facebook's data mining scandal.

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