Tesla CEO Elon Musk recently said that it’s an “open secret” in Silicon Valley that Apple is working on building some sort of vehicle. While Apple has not confirmed that this is the case, there are an increasing number of signs that suggest Musk is right. The Guardian reported last year that it came across documents that proved Apple was working on a self-driving car, and that the company had met with officials in California over the state’s self-driving car regulations. And now there’s another revelation: Apple has poached a Google employee that had been working on electric charging systems, potentially for its car project.

Today, it was a revealed that Google applied for a patent for an electric-vehicle charging system. According to research provided to Quartz by legal technology firm ClientSide, one of the inventors on the patent, Kurt Adelberger, has since left Google to work at Apple. According to Adelberger’s LinkedIn page, he’s listed as a product designer at Apple, but no employment information is listed beyond him leaving Google last summer. (Quartz has reached out to Apple for confirmation that Adelberger is now at Apple, and for more information on what he’s working on.)

Adelberger has had quite the career: Having trained as an astrophysicist at Harvey Mudd College and the California Institute of Technology, his 194 published research papers have been cited over 2,000 times. He’s most recently been working on energy storage and reducing the costs of charging electric vehicles, according to his LinkedIn page.

US Patent and Trademark Office Google’s proposed system.

The Google patent application outlines a device that would manage the connections between an electric vehicle and a charging station. It essentially determines how much charge the station has, and how much the car needs. The proposed device would also be able to figure out that, if the car needs to be connected for multiple hours to charge, electricity may be cheaper at a later time, and it will ensure the car doesn’t start charging until the price of energy has fallen.

It’s not exactly categorical proof that Apple is working on an electric car—Adelberger has worked on solar panels and other energy storage systems in his time at Google, and Apple is committed to running all of its facilities on renewable energy. But considering he was working on electric-vehicle technology before leaving Google, it seems a possibility. And Apple has been poaching automotive experts for a while now: It recently brought on a former Tesla and Aston Martin designer to work on “special products” and has poached hundreds of others from automakers, including Ford, GM, Toyota, and Tesla, and multiple battery companies.