Chelsea have signed Fiorentina left-back Marcos Alonso on a five-year contract for a reported £23m.
The 25-year-old uncapped Spaniard moves to the Premier League for the third time in his career.
Alonso played for Bolton 46 times from 2010 to 2013 before moving to Fiorentina and had a four-month loan spell at Sunderland in 2014.
"It's time for me to win some titles. It's a step up in my career," Alonso said on Chelsea's website.
Cesar Azpilicueta is the first-choice left-back at Chelsea, who have loaned Baba Rahman to Schalke this summer.