After five years of working at Tesla, Apple’s former VP of Mac hardware engineering, Doug Field, has returned to Cupertino — but apparently to work on Apple’s autonomous car initiative Project Titan.

Apple has officially acknowledged rehiring Field, but his specific involvement with Titan was confirmed to Daring Fireball by unnamed sources within the company. According to the report, Field is working alongside Bob Mansfield, a senior hardware engineering VP who briefly “retired” from Apple in 2012 yet remained involved in unnamed special projects for the company, including Titan.

Titan has been an unusually open secret for years. Reports have claimed that Apple has flip-flopped between advancing and scaling back the project, at one point working to develop an entire next-generation vehicle before deciding to focus more narrowly on specific autonomous systems. Company executives have winked in the project’s general direction, at one point describing cars as the ultimate mobile device, as if they represented a clear next step after Apple‘s successes with smartphones and tablets.

Field’s return to Apple comes amidst significant vehicle-related employee turbulence at both Apple and Tesla. Both companies have hired and lost numerous automotive experts in recent years, with Apple reportedly laying off hundreds of people during its 2016-2017 scaling back of car development plans. Tesla has experienced numerous departures related to the troubled launch of its entry-level Model 3.

During his prior five years at Apple, Field led hardware development for the redesigned iMac, MacBook Air,…