Tesla’s Chief Financial Officer, Zachary Kirkhorn, has resigned from his position after serving for four years. The announcement came from the world’s most valuable car company, which also revealed that Vaibhav Taneja, who was in charge of accounting, will take over the role. After this news, Tesla’s shares experienced a drop of over 3% on Monday.

The company led by Elon Musk didn’t give a particular reason for Zachary Kirkhorn’s departure. Kirkhorn has been part of Tesla (NASDAQ:TSLA) for 13 years. He will stay with the company until the end of the year to help make the transition to the new arrangement go smoothly.

Under his leadership, Tesla achieved its inaugural quarterly profit, driven by the launch of the mass-market Model 3 compact sedan. This success also led Tesla’s market value to surpass the $1 trillion milestone.

During a conference call to discuss the company’s quarterly results, Elon Musk unexpectedly announced Zachary Kirkhorn’s appointment and the departure of the previous CFO, Deepak Ahuja, in 2019.

In a LinkedIn post, Kirkhorn expressed, “Being a part of this company is a unique journey, and I take immense pride in the accomplishments we’ve achieved together since I became a part of it more than 13 years ago.”

Kirkhorn did not immediately respond to queries when contacted on LinkedIn.

Gene Munster, who manages Deepwater Asset Management, explained that Zachary Kirkhorn’s decision to stay until the end of the year probably means he’s leaving for personal reasons. One possible reason could be that working with Elon Musk has been tough, considering he’s been doing it for about 13 years.

At the age of 45, Vaibhav Taneja became a member of Tesla through the acquisition of SolarCity in 2016. Now, alongside his position as chief accounting officer, he has taken on the role often referred to as the “Master of Coin” at the company.

During this year, the car company based in Austin, Texas, decided to lower the prices of its vehicles. This choice aimed to increase sales and capture a larger market share, but it also reduced its previously industry-leading profit margins.

Tesla has also hinted at more price cuts in what Musk called “turbulent times” as rising borrowing costs take a toll on the sales of electric-vehicle makers.

Outgoing CFO Kirkhorn was also considered a possible successor to Musk earlier this year, the Wall Street Journal had reported amid growing investor concern about the lack of a clear succession plan.

Musk currently leads SpaceX, Neuralink, the Boring Company and is chief technology officer at social media platform X, formerly known as Twitter.