Chelsea have signed Papy Djilobodji from Nantes on a four-year contract.
Djilobodji, who was in the final year of his Nantes contract, can play at centre-back or in a defensive midfield role and sources earlier told ESPN FC that the clubs had agreed a £2.7 million fee.
The 26-year-old Senegal international had been at the French club since 2009, helping them to promotion in 2013 and going on to make 59 appearances in Ligue 1.
He told Chelsea's official website: "I'm very happy to sign for a big club like Chelsea and I want to do my best to help the team win titles. I want to thank the club for giving me this opportunity."
Chelsea had been in the market for a new centre-back this summer and turned to Djilobodji after failing in efforts to sign Everton's John Stones and Zenit St Petersburg's Ezequiel Garay.
The Premier League champions had already brought in Radamel Falcao, Pedro Rodriguez, Asmir Begovic, Baba Rahman, Kenedy, Nathan and Danilo Pantic this summer.
Meanwhile, Chelsea announced their 27th loan exit with Islam Feruz joining Scottish Championship side Hibernian for the season.
The 19-year-old is a Scotland under-21 international.