• Brian Acton, a co-founder of WhatsApp, has broken his silence about leaving Facebook three years after his company was acquired for $16 billion.
  • In an explosive interview with Forbes, Acton outlined tensions with Facebook CEO Mark Zuckerberg and COO Sheryl Sandberg about introducing ads into WhatsApp.
  • Acton recalled one meeting where Zuckerberg apparently told him, "This is probably the last time you'll ever talk to me."
  • He said he never became close to the Facebook chief, despite leading the company's most expensive acquisition.

WhatsApp co-founder Brian Acton has broken his silence about why he left Facebook last year in an explosive interview with Forbes--and it is a gnarly Silicon Valley fight for the ages.

Acton left Facebook in 2017, three years after the company acquired WhatsApp for $16 billion. His co-founder, Jan Koum, left in 2018 and is, according to Forbes, uncontactable while sailing in the Mediterranean.

Acton provided the first official confirmation that things were extremely icy between the WhatsApp team Facebook CEO Mark Zuckerberg and COO Sheryl Sandberg.

He recounted one meeting where he was dragged before Zuckerberg and Facebook's lawyers about how Facebook could make money from WhatsApp. The messaging app's founders have been famously reluctant to introduce ads into the service, but that's also Facebook's primary way of making money.

Brian Acton WhatsApp

WhatsApp co-founder Brian Acton, REUTERS/Mike Blake

Specifically, they wrangled over whether Facebook's insistence on introducing ads into WhatsApp meant that Acton could exit and take his full allocation of stock.

The $16 billion acquisition price comprised $4 billion in cash and $12 billion in Facebook shares. If Facebook ever introduced ads against the founders' will, Acton and Koum could take all their allocated stock before the agreed four-year period.

Facebook's lawyers didn't think exploring monetization broke the agreement. According to Acton, Zuckerberg told him, "This is probably the last time you'll ever talk to me."

Despite three years at Facebook and heading up its most expensive acquisition to date, Acton said he never became close to Zuckerberg. "I couldn't tell you much about the guy," he said.

This somewhat stacks up with other reports about Zuckerberg's personality--the kinder of them suggest he's close only to a small group of friends, while the less kind versions portray him as emotionless.

Acton's explosive account comes just as another pair of founders quit Facebook: Instagram founders Kevin Systrom and Mike Brier announced their departure on Monday, again after reported tensions with Zuckerberg.

--This post originally appeared on  Business Insider.