Cesc Fabregas has completed his transfer to Chelsea from Barcelona, the Spain midfielder has announced in a statement.
The 27-year-old is currently in Brazil with the national squad but has put pen to paper on a deal that sees him return to England after leaving Arsenal for the Nou Camp in 2011.
He is believed to have signed a five-year contract for a fee in the region of £30million.
With Barcelona having failed to win any silverware last season and the appointment of Luis Enrique as the new head coach, Fabregas was allowed to leave Spain and he revealed that Chelsea was his preferred option from those who had made their interest known.
"I considered all the other offers very carefully and I firmly believe that Chelsea is the best choice," he said.
"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.
"It was extremely important to me that this transfer was completed before the World Cup so that my mind will only be focused on hopefully helping my country try to retain the trophy."
I firmly believe that Chelsea is the best choice. They match my footballing ambitions with their hunger and desire to win trophies...
With fellow Spaniards Xavi and Andreas Iniesta for competition, Fabregas broke into the Barcelona side and ended his first season with four winners' medals before picking up the first league title of his career the following year.
He remained in Spain for a third season despite the interest from Old Trafford but has now made the decision to leave his boyhood club.
The signing will be seen as perfect timing for Chelsea following the end of Frank Lampard's long affiliation with the club and he becomes the first addition to Jose Mourinho's squad as the Portuguese looks to improve on last year's trophyless campaign.
Barcelona also ended last season empty-handed and, with Luis Enrique taking charge at what could be seen as a transitional period at the Nou Camp, Fabregas was allowed the leave and was quick to thank the club.
"Firstly I would like to thank everyone at FC Barcelona where I enjoyed three wonderful years," he added.
"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."
Fabregas is likely to be joined in west London by Spain team-mate Diego Costa before the start of the new season as the Athletico Madrid forward has long-been targeted by Mourinho to solve his goalscoring issues.