Chelsea have signed defender Mamadou Sarr from partner club Strasbourg for £12m.
The 19-year-old Frenchman has signed an eight-year deal and is eligible to play at this month's Club World Cup in the US.
Enzo Maresca's side start their tournament against LAFC on 16 June, before facing Brazilian side Flamengo on 20 June and rounding off the group stage against Tunisian champions ES Tunis on 25 June.
Chelsea and Strasbourg agreed a deal for Sarr in January, with a view to completing the transfer this summer.
He made 28 appearances in all competitions for Strasbourg this season.