Zach Kirkhorn, Tesla’s chief financial officer and “master of coin,” has announced plans to leave the company, ending a successful 13-year run that some thought would result in him taking over as CEO eventually.

Kirkhorn submitted his resignation last week, but the departure was announced Monday in a regulatory filing. He will stay with the company through the end of the year to support his successor.

Vaibhav Taneja, Tesla’s current chief accounting officer, will take over Kirkhorn’s role.

“Being a part of this company is a special experience and I’m extremely proud of the work we’ve done together since I joined over 13 years ago,” Kirkhorn wrote in a LinkedIn post. “As I shift my responsibilities to support this transition, I want to thank the talented, passionate, and hard-working employees at Tesla, who have accomplished things many thought not possible. I also want to thank Elon for his leadership and optimism, which has inspired so many people.”

No reason was given for Kirkhorn’s decision. He was, however, one of the few executives who has learned how to communicate with and work alongside Elon Musk. Earlier this year, the Wall Street Journal reported Kirkhorn was being eyed as a possible successor to Elon Musk as CEO (though Musk is not expected to step aside anytime soon).

That’s long way from his introduction to the financial world four years ago as CFO, when Musk said during a call that “Zach” would take the job. Some analysts had no idea who he was talking about at the time. (Prior to heading the company’s finances, he worked as an analyst.)

Kirkhorn has always operated in the background at Tesla, helping to transform the company into its current levels of success. Tesla was valued at $50 billion when he took the CFO job. Today, it’s worth $773 billion.