Chelsea took their pre-season spending spree to over Â£80 million ($136 million, 101 million euros) after completing the signing of Atletico Madrid defender Filipe Luis on Friday.
Brazilian left-back Luis is reported to have cost Â£20 million as Blues boss Jose Mourinho continues his expensive overhaul of a squad that finished last season without a major trophy.
The 28-year-old is Chelsea's second capture from Spanish champions Atletico this week following Spain striker Diego Costa's move to Stamford Bridge on Tuesday.
Costa arrived for Â£32 million, following hot on the heels of the Â£27 million signing of Spain midfielder Cesc Fabregas from Barcelona and the Â£2.4 million deal for Hajduk Split's Mario Pasalic.
Mourinho's heavy investment in rebuilding his team has been partially funded by the Â£40 million sale of Brazil defender David Luiz to Paris Saint Germain in June.
Luis impressed as Atletico won the Spanish title and reached the Champions League final last season and he fills the void in Chelsea's squad left by Ashley Cole's move to Roma.
He has signed a three-year contract with the Premier League club and will wear the number five shirt.
"This move is a dream come true for me. I now have the opportunity to play for Chelsea, and also in the Premier League," Luis told the club's website.
"I'm very happy and looking forward to getting started and giving my best for the team during the coming seasons."
Mourinho got a close look at Luis when Atletico knocked Chelsea out of the Champions League semi-finals last season.
His dynamic displays convinced Mourinho he was the ideal candidate to solve the left-back dilemma which has troubled him since Cole fell out of favour last season. (Also read: Turkish Club Besiktas Buy Demba Ba From Chelsea)
With Mourinho believing Cole was no longer playing well enough to start on a regular basis, he was forced to use Cesar Azpilicueta, a right-back by trade, out of position at left-back.
But Mourinho was determined to avoid a repeat of that make-shift situation and he moved quickly to tie up a deal for the Brazilian.
Luis joined Atletico from Deportiva La Coruna in 2010 and has made 98 appearances in all competitions for the Madrid side, winning the Europa League in 2012 and the Copa del Rey in 2013 before last season's title triumph.
He has four Brazil caps and was placed on Luiz Felipe Scolari's standby list for the 2014 World Cup.