Jerome Guillen, a long-serving, top-tier Tesla executive with an extensive automotive background and who has been overseeing development of its battery-powered Semi truck, has left the company.

Guillen, who joined Tesla in 2010, left his role as president of Tesla Heavy Trucking as on June 3, the Palo Alto, California-based company said in an SEC filing on Monday afternoon. “We thank him for his many contributions and wish him well in his future career,” the company said in the filing, without providing details about what he will do next. 

His departure comes just months after he took on the role of truck chief on March 11. “As Tesla prepares to enter the critical heavy trucks market for the first time, Mr. Guillen will now leverage his extensive background in this industry to focus on and lead all aspects of the Tesla Semi program, including the related charging and servicing networks,” Tesla said in a March 12 SEC filing.

Guillen didn’t immediately respond to a request for comment.

In more than a decade with Elon Musk’s electric vehicle powerhouse, Guillen held multiple high-profile roles for the company and was among the company’s most senior executives. His roles included overseeing Tesla’s automotive operations, global sales and service, engineering and he was program director for the breakthrough Model S sedan during the car’s development and initial production phase through 2013. 

His most recent task, readying the Tesla Semi truck for commercial sale, has run into challenges. Since first debuting a prototype of the big-rig in November 2017, the Semi has fallen far behind schedule, missing Musk’s initial target of selling it by the end of 2019. It’s unclear whether production and sales will begin this year or if it has been pushed back to 2022. That’s because the model appears to depend use of a larger, next-generation lithium-ion cell that remains in development.

Before joining Tesla, Guillen was director of business innovation for Daimler AG, which made a critical decision to buy battery packs and motors from Tesla in early 2009, a move that helped it avoid bankruptcy. Daimler also invested in Tesla prior to its June 2010 public listing. Guillen also worked on product development for truckmaker Freightliner, and he earned a PhD in mechanical engineering from the University of Michigan.

Tesla shares, which rose 1% to $605.13 on Monday, were little changed in after-hours Nasdaq trading following the company’s SEC filing.