Chelsea have signed left-back Marcos Alonso from Fiorentina, the Serie A club have announced.
The former Bolton defender began his career at Real Madrid and has also had a spell on loan at Sunderland.
A statement on Fiorentina's website read: "ACF Fiorentina announces that it has sold, outright, Marcos Alonso Mendoza to Chelsea Football Club."
Alonso's arrival gives Chelsea head coach Antonio Conte options at the back, with the possibility of Cesar Azpilicueta switching to right-back and Branislav Ivanovic playing in the centre of defence.
The Blues have also been linked with re-signing Brazil defender David Luiz, whom they sold to Paris St Germain for £50million prior to the 2014 World Cup, ahead of Wednesday's closure of the transfer window.
Spanish full-back Alonso has signed a five-year contract, Chelsea confirmed.
He becomes the Blues' fourth summer signing after France midfielder N'Golo Kante, Belgium striker Michy Batshuayi and Portuguese goalkeeper Eduardo.
Alonso said on chelseafc.com: "I'm very happy. It's a step up in my career and I think this is the perfect place for me to continue developing. It's time for me to win some titles.
"It was an easy decision for me to make when I heard the club were interested in signing me.
"My family and close friends know Chelsea is the club I have dreamed about playing for so I'm really excited about the challenge and I'm looking forward to working with my new team-mates."
Alonso played for Bolton for three seasons, including alongside Gary Cahill, who is now one of his Chelsea team-mates.