Chelsea have confirmed they've completed the signing of defender Kurt Zouma from Saint-Etienne.
The Frenchman will remain with his current club for the remainder of the season, and link up with his new Chelsea team-mates in the summer.
A statement on the official Chelsea website read: "Chelsea Football Club has today (Friday) signed Kurt Zouma from St. Etienne. He will remain on loan at the French club for the rest of the season.
"The 19-year-old central defender has joined Chelsea on a five-and-a-half year contract. This season he has made 12 league appearances for France's fourth-placed side."
Chelsea are believed to have paid around £12.5 million to secure the services of the 19-year-old, who has also been linked with Manchester United in the past.
Chelsea have been active in the January window, splashing €25 million to bring Nemanja Matic back to Stamford Bridge from Benfica, and around £11 million on Mohamed Salah from Basel.
So far they have also let Juan Mata leave to join rivals Manchester United, and Kevin de Bruyne depart for Wolfsburg.
It is unlikely that they will make any more new signings before the close of the January transfer window.
Zouma's arrival at Chelsea in the summer could cast doubt over John Terry's future - the 33-year-old is out of contract in the summer and is yet to agree a new deal.