The Brazilian defender has returned to Stamford Bridge from French giants PSG on a three-year deal.
Luiz, 29, departed West London for Paris two years ago for a fee of £50million but is now back in blue for a fee believed to be around £38m.
The Chelsea favourite told the club's official website: “I'm delighted to return to Chelsea. We had a fantastic story during my first time at the club and I want to help the team and Antonio Conte achieve a lot of success.
“I always had a wonderful relationship with the fans and I am looking forward to wearing the blue shirt at Stamford Bridge once again."
Welcome back, @DavidLuiz_4!
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— Chelsea FC (@ChelseaFC) August 31, 2016