London - English striker Patrick Bamford has returned to Middlesbrough from Premier League leaders Chelsea on a four-and-a-half-year contract, his new club announced on Wednesday.
"Middlesbrough have secured the signing of striker Patrick Bamford from Chelsea for an undisclosed fee," Middlesbrough announced on their website.
British media reports said Bamford had cost Boro around £6 million.
Bamford, 23, spent the 2014-15 season on loan at Boro, scoring 19 goals and being named Championship Player of the Year as Aitor Karanka's side made the play-off final.
He joined Chelsea from Nottingham Forest in January 2012, but has never played a game for the west London club.
As well as Boro, he has also spent time on loan at Milton Keynes Dons, Derby County, Crystal Palace, Norwich City and Burnley.
Chelsea recalled him from his loan spell at Burnley last week.
Bamford is Boro's second new signing of the January transfer window after Benin striker Rudy Gestede, who signed from Aston Villa two weeks ago.