After a deal to take the centre-forward to London from Atletico Madrid was announced earlier this month, the €44 million Spain international is now definitively a Blues player
A deal to take the Spain international from Atletico Madrid was officially agreed on July 1, but the centre-forward has now finalised the details to register as a Blues player.
Jose Mourinho's side have paid Atleti the Brazilian-born star's buyout clause, with the total outlay around €44 million [£35m], including agents' fees.
Costa exclusively revealed to Goal his reasons for joining the Blues in June, expressing his excitement at signing for "one of the greatest clubs in the world".
The 25-year-old's contract at Stamford Bridge will net him €190,000 [£150,000] per week.