Atletico Madrid striker Diego Costa has completed his transfer to Chelsea on a five-year deal.
The fee for the 25-year-old Spain international is understood to be £32m.
"I am very happy to sign for Chelsea," Costa said. "Everybody knows it is a big club in a very competitive league and I am very excited to get started in England."
Chelsea boss Jose Mourinho had made the addition of a "killer" striker a key priority during the summer.
The London club scored 71 goals in the league last season, 31 fewer than champions Manchester City, who finished four points ahead of them, as Fernando Torres, Demba Ba and Samuel Eto'o all struggled to find the net consistently.
Costa will rejoin international team-mate Fabregas following a disappointing World Cup campaign in which Spain exited the tournament at the group stage.