Cesc Fabregas said he has "unfinished business" in England as his transfer from Barcelona to Chelsea was confirmed.
Fabregas, 27, who has signed a five-year contract, also said he had "rejected offers" from other clubs to move to Chelsea in a deal reported to be worth 33 million euros.
The Spain midfielder's return to the Premier League had been expected after three up and down seasons at the Camp Nou. Even last summer he took his time before deciding to reject a reported big-money offer from Manchester United and stay for another season in La Liga.
A switch this summer appeared imminent after club and country colleague Gerard Pique was caught on camera last week telling national coach Vicente Del Bosque that a deal had been agreed.
The confirmation was announced by both clubs on Thursday afternoon, with the new Blues No. 4 saying that he had chosen Chelsea due to the club's ambitions, their strong squad and manager Jose Mourinho.
"Firstly I would like to thank everyone at FC Barcelona where I enjoyed three wonderful years," Fabregas said on his new club's official website. "It was my childhood club and I will always be proud and honoured that I had a chance to play for such a great team.
"I do feel that I have unfinished business in the Premier League and now is the right time to return. I considered all the other offers very carefully and I firmly believe that Chelsea is the best choice.
"They match my footballing ambitions with their hunger and desire to win trophies. They have an amazing squad of players and an incredible manager. I am fully committed to this team and I can't wait to start playing."
Barcelona's statement on the move thanked the player for his efforts during the last three seasons and wished him the best for the future.
“I do feel that I have unfinished business in the Premier League and now is the right time to return.”
"FC Barcelona and Chelsea FC have reached an agreement for the transfer of player Cesc Fabregas to the English club," the statement said.
"FC Barcelona wishes to publicly thank Cesc Fabregas for his professionalism and dedication during his years at the club, which will always be his home, and to wish him all the very best for the future."
This is the second time that Fabregas departs from Barca -- having first left the club's youth system as a 16-year-old back in 2003 to join Arsenal.
Following eight seasons with the Gunners he returned to the Camp Nou in 2011, but never quite seemed to be a leading figure despite playing under three coaches in Pep Guardiola, Tito Vilanova and Gerardo Martino.
Fabregas did however win six trophies during these three years, including the 2012 Copa del Rey and 2012-13 La Liga title, scoring 42 goals in 151 games.
Barca are now expected to soon announce the signing, for around 20 million euros, of Croatian playmaker Ivan Rakitic as an replacement for their departing midfielder.
Fabregas is a key member of the Spain squad at the upcoming World Cup, where he will feature alongside new clubmates Fernando Torres and Cesar Azpilicueta, as well as reported Chelsea target Diego Costa.