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London, England (SportsNetwork.com) - Chelsea have completed a deal to sign midfielder Nemanja Matic from Portuguese side Benfica, the Premier League outfit confirmed on Wednesday.

Matic, 25, returns to Stamford Bridge for a transfer fee believed to be 21 million pounds after leaving the club for Portugal three years ago.

"I am very happy for this opportunity. I just want to say I will give my best to help the team and make the Chelsea fans happy," Matic said.

The Serb originally joined the Blues from Slovakian club MFK Kosice on a four- year deal for 1.5 million pounds in 2009.

He made two substitute appearances in the Premier League and was an unused substitute in Chelsea's 1-0 win over Portsmouth in the 2010 FA Cup final.

The midfielder re-joins the Blues on a new five-and-a-half year contract.

"He has grown as a player in Portugal and has become a fantastic all-around midfielder," Chelsea manager Jose Mourinho remarked.