After months of speculation, The Guardian revealed correspondences on Friday that seem to prove once and for all that Apple is building a car. The first time we reported on the possibility of an Apple car, it was shortly after a van with cameras had been spotted driving around San Francisco.

The newly uncovered documents show that since then, Apple has been making significant progress on a project which still remains tightly under wraps.

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According to the report, engineers working in Apple’s Special Project group met with officials from GoMentum Station in May to discuss renting out the facility. GoMentum Station is located in Concord, California, and among other things, currently serves as a testing ground for AVs (autonomous vehicles) aka self-driving cars.

“We would … like to get an understanding of timing and availability for the space, and how we would need to coordinate around other parties who would be using [it],” Apple engineer Frank Fearon wrote to the owners of GoMentum Station in an correspondence obtained by The Guardian.”

Fearon’s message continues: “We are hoping to see a presentation on the … testing grounds with a layout, photos, and a description of how the various areas of the grounds could be used.”

As The Guardian astutely observes, several other companies, including Google and Tesla, have obtained licenses to operate their own autonomous vehicles on public roads, but it required them to disclose key information about their vehicles that Apple might want to keep out of the public eye. Thus the top-secret testing facility.

“We had to sign a non-disclosure agreement with Apple,” Randy Iwasaki, owner of GoMentum Station, told The Guardian. “We can’t tell you anything other than they’ve come in and they’re interested.”

There’s no telling how long it will be until Apple is ready to make an official announcement regarding its future in the automotive industry, but something is definitely stewing behind closed doors. Be sure to visit The Guardian for the full story.