Real Madrid and Croatia midfielder Mateo Kovacic has joined Chelsea on a season-long loan.
Kovacic joins the Blues as goalkeeper Thibaut Courtois makes his permanent move in the opposite direction.
The 24-year-old has spend the last three seasons at Real since joining from Inter Milan.
He also helped Croatia reach the final of the recent World Cup in Russia.
“I am really happy and excited to be here. It is an amazing feeling,” Kovacic told Chelsea’s website.
“I will try to do my best for this club. It is a new league for me, the beginning is always tough but I am sure the coach and my new team-mates will help me and I am looking forward to a great season.”
Chelsea director Marina Granovskaia added: “He is a perfect fit for us this season, his style is well suited to how Maurizio wants to play and we are sure he will prove to be a valuable asset for the club.”
Kovacic is the second-youngest player ever to have scored in the Champions League after picking up a goal against Lyon aged just 17.