Tesla Inc. said on Monday that Zachary Kirkhorn stepped down as its chief financial officer and named its accounting head, Vaibhav Taneja, as its new CFO.

Kirkhorn, 39, a company veteran of 13 years, stepped down from the role on Friday, although he will remain with Tesla through the end of the year.

The Elon Musk-led firm did not specify a reason for Kirkhorn’s departure.

“During his tenure, Tesla has seen tremendous expansion and growth. Tesla thanks Mr. Kirkhorn for his significant contributions,” Tesla said in a regulatory filing Monday.

Kirkhorn said in a LinkedIn post: “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.”

Taneja, 45, has been Tesla’s accounting chief since 2019. He held other roles at the EV maker before that and previously worked at PricewaterhouseCoopers in India and the U.S.

Tesla shares turned negative on the news and closed down 1 percent at $251.45 on Monday. The stock price has doubled so far this year.

Kirkhorn’s departure comes as Tesla builds a new factory in Mexico and prepares to bring its Cybertruck pickup to market as it fends off rivals in the increasingly crowded EV market. Tesla has lowered prices across its lineup to maintain its position atop the electric-car industry.

“He’s done a 13-year tour of duty working for Elon, which is like working 50 years for anyone else,” said Gene Munster, managing partner of Deepwater Asset Management. “The fact that he’s sticking around until the end of the year bodes well for the transition.”

Still, the departure of Kirkhorn, who was considered a top contender to succeed Musk as CEO, renews uncertainty over leadership at Tesla. It also instantly raises the profile of Taneja, who wasn’t among the 16 executives invited on stage with Musk at an investor meeting in March.

Kirkhorn joined Tesla in 2010 as a senior financial analyst and was promoted five times, most recently to CFO in early 2019 at the age of 34. Before he took over, Tesla had a long history of losses and occasionally burned more than $1 billion of cash per quarter. The company has been consistently profitable since then and repaid about $10 billion of debt in the last three years, helping it secure investment-grade ratings. It also joined the S&P 500 Index in December 2020.

Before Kirkhorn took over as CFO in early 2019 at the age of 34, Tesla had a long history of losses and occasionally burned more than $1 billion of cash per quarter. The company has been consistently profitable since then and repaid about $10 billion of debt in the last three years, helping it secure investment-grade ratings.

Kirkhorn, a graduate of the University of Pennsylvania, worked under his predecessors as CFO, Deepak Ahuja and Jason Wheeler. He spoke at length on Tesla’s quarterly earnings calls and was well-regarded by investors for reining in costs. He regularly talked about how recurring revenue from software would play an increasing role going forward.

“Zach did a great job expanding margins,” said Munster. “Usually when companies scale up production, their margins come under pressure. He threaded the needle, and that’s a hard thing to do.”

Kirkhorn owned 197,540 shares of Tesla as of last month, according to data compiled by Bloomberg, a holding valued at about $49 million. He recently sold about $1 million of shares.

Kirkhorn added “Master of Coin” to his job title in early 2021, about a month after Tesla disclosed it had made a $1.5 billion investment in Bitcoin. The tongue-in-cheek title was given at the same time Musk became “Technoking of Tesla.”

The company’s filing Monday did not mention “Master of Coin” as one of Taneja’s roles as new CFO.

Bloomberg and Reuters contributed to this report.