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.
The £71m fee for Havertz includes add-ons.
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 of the summer.
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).
Chelsea look to Mendy
Chelsea are interested in signing Rennes goalkeeper Edouard Mendy to increase competition for Kepa.
They have already had one bid rejected by the French club for the 28-year-old from Senegal.
It is understood the interest in Mendy is not in order to replace Kepa, who was dropped by Lampard last season.
But with second-choice keeper Willy Caballero turning 39 later this month, the club wants a younger challenger to their number-one choice.
Reports suggest Rennes want more than £30m for Mendy.
Alistair Magowan, BBC Sport
Having been unable to sign players last summer because of a transfer ban, Chelsea have certainly made up for lost time.
Havertz's signing takes Chelsea's summer spending to almost £200m.
That will mean more is expected of Lampard, whose team finished fourth in the Premier League last campaign in his first season and were FA Cup runners-up.
There will also be questions about how much playing time some of Chelsea's academy graduates get, having made their breakthroughs last season when the transfer ban was still in force.
Find all the latest football transfers on our dedicated page.
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