Elon Musk was the reason one of Apple's most famous developers left Tesla after only six months

Earlier this week, $4 Chris Lattner left the company after not quite six months on the job.

A source close to the situation tells Business Insider that Lattner loved his job at Tesla, but that he and Tesla CEO Elon Musk didn't get along.

So, after six months of butting heads, the "decision was mutual" for him to leave, this person said. The departure was something between an up-and-quitting and being asked to resign.

Tesla hinted at the latter with its statement confirming Lattner's departure: "Chris just wasn't the right fit for Tesla, and we've decided to make a change. We wish him the best."

Lattner joined Tesla in January after 11 years at Apple; Tesla is known $4. According $4 it is even hoping to move into Apple's old campus in Cupertino, California, after Apple moves $4.

Even so, Tesla's$4 made headlines. Lattner is famous in the software-development world as the creator of Apple's enormously popular programming language called Swift.

The person we spoke to wouldn't share the details of what caused tension between Lattner and Musk. But there was a hint in who it chose to replace Lattner: a hardware guy, Jim Keller. Keller is a legendary chip architect who once worked for AMD and now "has overall responsibility for Autopilot hardware and software," Tesla says.

So the focus of the team seems to be on hardware.

Tesla is developing its own Autopilot hardware after chip supplier Mobileye chose not to renew its contract with Tesla some months after a Model S owner $4 while Autopilot was activated.

The new hardware requires new software.

For the software portion, it hired Andrej Karpathy, a guy known to be a brilliant scientist in computer vision and deep learning, but who lacks the experience running a team of building software on deadlines for commercial uses.

Karpathy will report directly to Elon Musk. The good news? He already has experience working with the $4 Musk. Karpathy was working as a research scientist at Musk's non-profit OpenAI. That's a group co-founded by Musk to develop artificial intelligence technologies. Musk serves at its chairman.

As $4, in the last seven months, three executives overseeing the Autopilot software have left the company: Sterling Anderson, David Nistér and now Lattner. And that's raising eyebrows given some of the public promises Musk has made for the new Autopilot system, including a vow last October that a Tesla car will drive autonomously from $4 by the end of the 2017.

As for Lattner, we heard that Uber contacted him immediately for its self-driving program and the option to return to Apple may still be available, but that he hasn't chosen his next move yet.

When we reached out to Lattner for comment, he pointed us to his $4. In it, he said: "Overall I learned a lot, worked my butt off, met a lot of great people, and had a lot of fun. I'm still a firm believer in Tesla, its mission, and the exceptional Autopilot team: I wish them well."

Tesla has not yet responded to our request for additional comment.

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