'The transfer will be subject to the agreement of personal terms and a medical'.
And with that, the striker is no longer a Premier League footballer, much like the past few months in truth...
With relations between player and club at a breaking point, Costa refused to return to west London as he remained AWOL in Brazil - the land of his birth.
Earlier this summer, in an interview with ESPN Brasil, Costa accused Chelsea of pricing him out of his desired move back to Atletico, but the clubs have now agreed on a fee.
The Spanish striker was once again an integral part of a Blues' title triumph, hitting 20 goals in 33 appearances.
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At the time Costa seemed on the verge of signing a lucrative deal with Chinese Super League club Tianjin Quanjian.
Now Costa is heading back to Atletico Madrid, with claims from Spain that the club will pay Chelsea an initial €55m and a further €10m in potential bonus payments.
The Brazilian scored Chelsea's first and his first goal since March 2016 when he ghosted behind the Forest defence to meet Antonio Rudiger's cross with a side-footed shot that beat goalkeeper Stephen Henderson.
Costa can't play for Atletico now because the club was banned by Federation Internationale de Football Association from registering new players until 2018, for having broken rules regarding the transfer of underage players.
Costa has not featured for the Premier League Champions since the FA Cup final loss to Arsenal in May.