Tesla (TSLA 0.38%) has lost one of its upper-level executives. In a tersely worded regulatory filing submitted on Monday, the prominent electric-vehicle (EV) producer said that its heavy-duty trucking unit president, Jerome Guillen, had departed, effective last Thursday, June 3. Tesla did not provide a reason for the departure.

Guillen had been at Tesla for quite some time, although he only served in his present capacity since this past March.

A Tesla Semi on the road.

Image source: Tesla.

According to his LinkedIn page, he started at the company in late 2010 as the program director for its premium Model S sedan. During his tenure at Tesla, he filled other managerial roles such as vice president of worldwide sales and service, president of the automotive division, and acting vice president of vehicle engineering.

Tesla is, of course, known for its passenger vehicles such as the Model S and the Models X and Y SUVs. It has moved into larger vehicle categories, most notably with the Cybertruck pickup. In terms of heavy trucks, in 2017 it took the wraps off its Tesla Semi, a predictably sleek-looking EV that the company claims can save over $200,000 in fuel costs, and has a two-year payback period.

That sales pitch seems to be landing with notable companies such as Walmart and PepsiCo, which have made relatively small-scale Tesla Semi orders. So the heavy-duty trucking unit seemed to be on the rise, making Guillen's departure somewhat mysterious.

It didn't seem to spook Tesla believers, though. The company's stock rose by 1% on Monday, well outpacing the generally flat performance of the S&P 500 index on the day.