Bearing in mind subsequent changes (including the 2020 phase-out currently in the works), a 2013 press release by Northrop Grumman said:
Turkish Aerospace Industries, Inc. (TAI), a subcontractor to Northrop Grumman, delivered its first F-35 Lightning II center fuselage to Northrop Grumman and Lockheed Martin at a ceremony held at TAI's facilities in ...
According to Turkish Aerospace Industries (TAI)
One of the most complex structural sections of the aircraft, "F-35A Center Fuselage" is produced by TAI as a second source.
Second source means "a company that is licensed to manufacture and sell components originally designed by another company (the first source)"
The F-35 made by Lockheed Martin is a joint venture by multiple countries; among others, USA, Canada, Italy and Turkey.
Turkey was part of the deal and they helped funding the development of the jet. They were expelled from the program after the deal to buy the Russian S-400 missile defense system.
Ellen Lord, Pentangon acquisition chief, commenting on the ...