Chelsea have signed attacking midfielder Kai Havertz from Bayer Leverkusen on a five-year contract in a deal worth about £71m.
The Germany international has scored 36 goals and contributed 25 assists in 118 appearances for the Bundesliga club.
He is Chelsea's second most expensive signing after Kepa Arrizabalaga joined from Athletic Bilbao (£71.6m) in 2018.
"I am very happy and proud to be here. It is a dream come true to play in a big club like Chelsea," said Havertz.
Chelsea director Marina Granovskaia said: "Kai is one of the best players of his age in world football, so we are very happy that his future lies at Chelsea.
"He is an exciting, dynamic talent. We are delighted to be able to add his versatility and quality to the squad before the season begins."
Havertz, 21, is Blues manager Frank Lampard's seventh signing in his first window since the club's transfer ban was lifted.
He follows forward and compatriot Timo Werner, midfielder Hakim Ziyech, and defenders Xavier Mbuyamba, Malang Sarr, Ben Chilwell and Thiago Silva to Stamford Bridge.
Sarr will be loaned out, while Mbuyamba has gone into the Blues' Under-23 squad.
Having graduated from the Leverkusen academy, Havertz scored 18 goals in 45 appearances last season, including eight in the 11 games after the campaign restarted.
The versatile midfielder, who can also play up front, has scored once in seven appearances for Germany.
Chelsea begin their Premier League campaign away at Brighton on Monday, 14 September (20:00 BST).