Striker Loic Remy has joined Chelsea from QPR on a four-year deal, the two clubs have announced.
Remy becomes a Blues player after they activated a release clause in the France international's contract.
He arrives at Stamford Bridge as Fernando Torres departs, with the Spain frontman having gone to Italy to join AC Milan on a two-year loan.
Remy said on www.chelseafc.com: "I feel very happy and very proud.
"When I heard Chelsea wanted to sign me I said 'let's go' straight away because they are one of the best clubs in the world.
"I remember the amazing atmosphere at Stamford Bridge when I played there for Marseille and I can't wait to play for the first time in front of my new fans."
It is understood Chelsea, triggering the release clause, are paying £10.5million for Remy, who had looked set to join Liverpool earlier this summer.
The proposed switch to Anfield broke down following a medical, but Chelsea boss Jose Mourinho said of the 27-year-old on Saturday: ''The information we have from specialists in different areas is he doesn't have a problem to play football.''
Remy came through Lyon's youth academy and, after a loan spell at Lens, moved on to Nice and then Marseille, from whom he signed for QPR in January 2013.
He scored six goals in 14 games for Rangers that season, but was unable to prevent them from being relegated from the Barclays Premier League.
He made a swift return to the division in 2013/14, spending the campaign on loan at Newcastle and scoring 14 goals.
Remy then featured in QPR's first two games this term as they made their top-flight comeback, but was missing from the squad for Saturday's 1-0 home win over Sunderland as the completion of his move to Chelsea drew near.
He also sat out Rangers' Capital One Cup game earlier in the week, meaning he will be eligible for his new club in all competitions.
It was reported on Saturday evening that Arsenal had made an enquiry about Remy, but interest had been withdrawn by Sunday.
Meanwhile, AC Milan announced on Sunday that Torres' switch to the San Siro was complete, with him having signed a contract through to June 2016.
Milan were poised to complete a second signing from Chelsea late on Monday, confirming that midfielder Marco Van Ginkel had arrived in the city.
"Dutch midfielder Marco Van Ginkel arrived at the Milan-Linate Airport at 22.40 local time," the club said on their website.
No details about his move were given, but it is expected the 21-year-old will join on a season-long loan.