David Datro Fofana said he has joined "the club of my dreams" after completing the formalities of a move to Chelsea from Norwegian side Molde.
Chelsea reached an agreement to sign Ivory Coast international Fofana last month in a reported £10.5million (€12m) deal.
That transfer officially went through on Saturday, with the 20-year-old signing a six-and-a-half-year contract that contains the option of a further 12 months.
Boyhood Chelsea fan Fofana told the club's website: "I'm here, I've arrived well and I'm very happy to sign for the club of my dreams. I'll see you soon on the pitch. Cheers!"
Fofana, who has three senior international caps, top-scored for Molde with 15 goals last season as they regained the Norwegian Eliteserien title.
He played a part in 34 goals in 65 appearances for Molde, with 24 goals and 10 assists in all competitions since joining at the start of the 2021 campaign.
Chelsea announced the signing of defender Benoit Badiashile from Monaco on Thursday, while a deal has also been struck for Brazilian youngster Andrey Santos.