The 30-year-old Brazil-born player is the club´s first signing since the appointment of Luiz Felipe Scolari as manager and he is believed to have cost around £8million.
Deco told Chelsea TV: "It is good for me to be here and first of all I am very happy to be here. I am sure I have come at the right time to do great things and be able to help Chelsea go back to the way it was and come back to being the first one, not only in England but also to win the Champions League that has been their dream for so long."
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