Chelsea have broken the world record transfer fee for a goalkeeper by signing Kepa Arrizabalaga from Athletic Bilbao for £71.6m on a seven-year deal.
The 23-year-old arrives on the eve of Thibaut Courtois' departure from Stamford Bridge, with the Belgian set to be unveiled at Real Madrid on Thursday after he undergoes a medical.
Having activated Kepa's release clause earlier on Wednesday, Chelsea's £71.6m deal surpasses the £67m Liverpool spent to bring Alisson Becker to Anfield earlier this summer.
Kepa will train with his new team-mates for the first time on Thursday, and will be available for their Premier League opener against Huddersfield on Saturday.
"It's a very important decision for me, for my career, and also for my personal life," Kepa told Chelsea's club website.
"So many things attracted me to the club, all the titles the club has won, the other players, the city, the English Premier League. It's an accumulation of things, and I am very glad Chelsea has decided to trust me and to take me in as well."
Kepa featured 30 times for Athletic in La Liga last season, keeping seven clean sheets, with his form earning him a call-up to Spain's World Cup squad after making his national team debut last November.
He becomes the sixth Spaniard in Chelsea's squad, joining Cesar Azpilicueta, Marcos Alonso, Cesc Fabregas, Pedro and Alvaro Morata.
Chelsea director Marina Granovskaia added: "Kepa is a talent we have admired for a long time and we are extremely excited about his arrival.
"He has already demonstrated fantastic quality and consistency and will be a big part of any success Chelsea have in the coming years.
"His long-term contract reflects the belief we have in him and we look ahead to the coming seasons with an enormous sense of optimism."