Radamel Falcao will return to the Premier League next season after agreeing terms to join champions Chelsea on a temporary basis.
The Colombia international moved to Manchester United last September, signing a year-long loan at Old Trafford.
Chelsea manager Jose Mourinho has previously hinted the club could make a move for the striker, and on Friday the switch was confirmed.
Falcao told Chelsea's official website: "I am very happy to be joining Chelsea and can't wait to start training and help with our aim of retaining the league title and being successful in Europe."
That led to his move to Ligue 1 with Monaco, however, the forward struggled to settle in France and, after being unable to find his feet with United, will rook to revitalise his career at Stamford Bridge under the guidance of Mourinho.
Chelsea now boast four players who have spent time at Atletico, with Falcao joining Costa, Filipe Luis and goalkeeper Thibaut Courtois at the club.
Croatian midfielder Mario Pasalic - who joined Chelsea from Hajduk Split last year - will go the other way to spend the 2015-16 season at Monaco.
