The Croatia international has joined on a temporary deal as part of the same move for goalkeeper Thibaut Courtois to head to Real Madrid.
Kovacic has signed for the Blues on a season-long loan deal and will now be hoping to hold down a spot in the first team at Stamford Bridge under new manager Maurizio Sarri.
The 24-year-old made five appearances for Croatia as he helped his country to reach the World Cup final in Russia this summer.
And the attacker has revealed his delight at putting pen to paper on his temporary transfer to the west London club.
Speaking in an interview with Chelsea FC’s website, Kovacic said: “I am really happy and excited to be here at Chelsea. It is an amazing feeling.
“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 FC will be aiming to be one of the main contenders for the Premier League title next season after they ended up in fifth place last term under Antonio Conte.
The Blues managed to win the FA Cup last term but they will have to make do with Europa League football this time around after they failed to finish in the top four in Conte’s final campaign in charge.
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