Striker Diego Costa has completed his move back to Atletico Madrid from Premier League champions Chelsea.
The two clubs agreed terms last week and the 28-year-old Spain international passed his medical on Monday.
Costa cannot be registered to play for the La Liga side until 1 January, when the club's transfer window ban comes to an end.
However, Atletico said he will begin training immediately and is likely to be in the stands when Chelsea are the visitors for the first ever Champions League game at Atletico's new Wanda Metropolitano on Wednesday.
Costa left Atletico for Chelsea in 2014 and scored 59 goals in 120 games appearances for the Blues.
He won two Premier League titles and the League Cup with the club, but found himself exiled at Stamford Bridge over the summer.