Christopher Nkunku says he is "incredibly happy to be joining Chelsea".
The Blues completed his signing from RB Leipzig for £52m on Tuesday.
"A big effort was made to bring me to the club and I am looking forward to meeting my new coach and team-mates and showing the Chelsea supporters what I can do on the pitch," said Nkunku.
"Having played in Ligue 1 and the Bundesliga, I now want to play in the Premier League, one of the strongest leagues in the world. I am very excited for this challenge and will be proud to wear the Chelsea shirt."