Sergio Aguero has joined Barcelona on a two-year contract the Catalan club has announced.
The Argentine 32-year-old leaves City after 10 years at the club, during which he became their all-time leading goalscorer with 260 goals in 390 games.
His last appearance came off the bench in Saturday's 1-0 Champions League final defeat by Chelsea.
Aguero, who won 15 major trophies during his time in Manchester, will join compatriot and close friend Lionel Messi at the Nou Camp as the Catalan club look to improve on a third-place finish in La Liga.
European champions Chelsea were linked with a move for Aguero, but he has opted to return to a league in which he scored 74 goals in five seasons for Atletico before his £36m move to City in 2011.
"We all know that Barcelona are the best club in the world," said Aguero.
"I think I made a great decision to be here and of course it is a step forward in my career.
"I am really happy and hopefully I can help the team to win things."
Eric Garcia and Georginio Wijnaldum have also been linked with free-transfer moves to Barcelona.