Not too long ago, Apple and Google announced that they were partnering up to launch a contact tracing initiative to help stop the spread of the global coronavirus pandemic.

Since then, we’ve learned a few more details about the program, including the fact that Apple and Google have decided to change the market branding to “exposure notification” rather than contact tracing, and details regarding the user privacy of the system. But how did it all come together? Well, up until now, those details have been a mystery.

CNBC has shed some light on how the relationship between the companies in this particular regard came to be. And it actually starts with another company completely. Edouard Bugnion, the CTO VMWare, apparently reached out to Apple to talk about contact tracing, and how privacy and general usability would remain the focus of such an effort. Bugnion’s comments made their way to Apple’s Myoung Cha, who is responsible for the business side of Apple’s health efforts and who answer’s to Apple’s Jeff Williams.

It turns out that Cha was already developing ideas for how smartphones could be used for contact tracing, which was known as “Bubbles” within the company. That initial team included members like Dr. Guy, Apple’s VP of privacy, and Ron Huang, boss of the company’s location services, among others.

But things blew up from there:

Within a few weeks, the Apple project — code-named “Bubble” — had dozens of employees working on it with executive-level support from two sponsors: Craig Federighi, a senior vice president of software engineering, and Jeff Williams, the company’s chief operating officer and de-facto head of healthcare. By the end of the month, Google had officially come on board, and about a week later, the companies’ two CEOs Tim Cook and Sundar Pichai met virtually to give their final vote of approval to the project.

A similar project was being developed at Google, too, codenamed “Apollo”. That eventually went up the food chain at the company as well, and, ultimately, Google’s VP of Android, Dave Burke, reached out to Cha at Apple. One thing after another and Apple’s CEO, Tim Cook, was part of a video conference call with Google’s CEO, Sundar Pichai, and, voila, the partnership between the two companies for a contact tracing effort was given the green light.

It wasn’t a foregone conclusion that the two companies, which have a long history of bitter competition in smartphones, would cooperate. Apple co-founder Steve Jobs was convinced that Android had been built to mimic Apple’s iOS, and the two companies had a bitter legal fight before settling their differences in 2014. Although they coexist more peacefully now, they’re still tough rivals, with the two dominant smartphone platforms in the world.

But in this case, they knew they had to come together. A system for exposure notification needed to be interoperable, otherwise there would be huge gaps in coverage.

The two companies couldn’t formally announce plans to work together until they got a green-light from their CEOs. So Apple CEO Tim Cook and Alphabet CEO Sundar Pichai hashed it out on a virtual meeting several days ahead of the official announcement on April 10th.

The full report is absolutely worth a read if you’re curious about how this all came to be.

Apple and Google’s first beta of the exposure notification system is set to arrive soon.