Chelsea have re-signed midfielder Nemanja Matic from Benfica on a five-and-a-half year contract.
The 25-year-old made the switch to Benfica in 2011 as part of the deal that saw centre-back David Luiz move to Stamford Bridge.
Matic confirmed his intention to depart the Estadio da Luz on Tuesday, and Chelsea have confirmed on Wednesday that he has re-joined them on a long-term deal.
"I am very happy for this opportunity to be back at this club," the Serbia international told Chelsea's official website.
"I feel very good because of that and just want to say I will give my best to help the team and make the Chelsea fans happy."
Although Chelsea did not confirm the fee involved in the transfer, Benfica announced to the Portuguese stock exchange they had agreed a deal worth €25million with the Londoners.
Chelsea manager Jose Mourinho said he was "very pleased" to see Matic return.
"He has grown as a player in Portugal and has become a fantastic all-round midfielder," he told the club's official website.
"I am sure he will become a very important member of the squad and help us to achieve our ambitions."
Matic was named Primeira Liga Player of the Year last season, and was part of the Benfica side that lost 2-1 to Chelsea in the UEFA Europa League final in May.
Chelsea originally signed the midfielder from MFK Kosice in 2009, but he made just two Premier League appearances for the London club.
He then made 27 appearances while on loan at Eredivisie outfit Vitesse in the 2010-11 campaign, before joining Benfica in January 2011.