In a statement released on Chelsea's official website, the Blues confirmed the news which has been swirling around in the rumor mill for quite some time.
Kovacic will join Chelsea on loan until June 30, 2019 as part of the deal, with the Croatia global spending a season away from the club he joined from Inter Milan in 2015.
Sources told ESPN FC that Kepa boarded a flight from Bilbao Airport on Tuesday, with Spanish newspaper AS reporting that he is set to meet with his representatives in Madrid and decide whether to make the move to Stamford Bridge.
Courtois, who had less than a year left on his Chelsea contract, wanted to move to Spain for personal reasons.
Courtois has been at the west London club since 2011, and wrested the No. 1 jersey from club favourite Petr Cech after shining during a loan spell with Atletico Madrid as a youngster.More news: Arsenal near deal to sell Lucas Perez to West Ham
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The 26-year-old appeared unwilling to wait a further 12 months to grant his move with Sarri publicly telling Courtois to confront him personally if he wishes to leave the club. It's a curious twist of fate that his departure from Stamford Bridge would pave the way for Kepa, who was so close to joining the European champions in January, to go the opposite way and replace the Belgian at Chelsea.
The goalkeeper arrives as the club's record signing and the most expensive stopper in world football.
World Cup finalist, Mateo Kovacic on the other hand, will spend a season on loan at Chelsea. The Croatian midfielder competed with regular Madrid starters Casemiro, Toni Kroos and Luka Modric.
He becomes the third acquisition of a chaotic summer transfer window for Chelsea, following the £50m capture of Jorginho from Napoli and the signing of third-choice goalkeeper Robert Green on a free transfer.
Chelsea will start their EPL campaign with a game against Huddersfield on Saturday.