Brazilian defender Alex has completed his move from PSV Eindhoven to Chelsea.
Alex played for Brazil in the Cop America
"Alex Rodrigo Dias da Costa has passed a medical and signed a three-year contract with Chelsea," said a statement on the Chelsea website.
Alex added: "I'm happy for the opportunity Chelsea have given me. I hope to start very soon and to do a good job at this wonderful club."
The 25-year-old Alex, who began his career at Santos, helped PSV win three successive Dutch league titles.
The defender played in the Brazil side that won the Copa America with victory over Argentina in the final in Venezuela on 15 July.
The Blues had to loan Alex to PSV Eindhoven after buying him in 2004 because he had not played enough games for Brazil to qualify for a permit.
Alex is hoping manager Jose Mourinho and defender Ricardo Carvalho, who are both Portuguese, will help him settle at Chelsea.
"I hope to adapt myself very quickly because Carvalho and Mourinho will help me with the language barrier."