Apple (NASDAQ:AAPL) and Chinese automaker BYD (OTCPK:BYDDF) worked secretly for years as part of the technology firm’s now-canceled car project, Bloomberg reported, citing people familiar with the situation.

For years, Apple was rumored to be working on a futuristic self-driving car, with the company tied to collaborations with Volkswagen and even a potential deal to buy McLaren at one point. That never happened and the project was canned after 10 years,

Bloomberg reports that in 2017, Apple and BYD reached an agreement to create batteries using lithium iron phosphate cells (LFP), which would have increased the car’s autonomy and provided a safer alternative to typical electric vehicle batteries.