Kai Havertz has joined Chelsea from Bayer Leverkusen for a fee of £75.8m (€85m) after signing a five-year deal.
Havertz becomes Frank Lampard's seventh summer addition, joining Germany team-mate Timo Werner, Hakim Ziyech, Ben Chilwell, Thiago Silva, Malang Sarr and Xavier Mbuyamba.
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"I am very happy and proud to be here," Havertz said. "For me it is a dream come true to play in a big club like Chelsea and I can't wait to meet all the players and the trainers. Yeah, I am very happy to be here!"
The 21-year-old midfielder completed his medical with Chelsea on Sunday in London before joining up with Germany for their Nations League fixtures.
Havertz was in Stuttgart with Germany's squad for their UEFA Nations League fixtures, having been an unused substitute as they drew 1-1 with Spain on Thursday night.
Both Bayer Leverkusen and Germany confirmed Havertz's departure on Friday morning, with the club thanking the national side for cooperating.
As part of the deal, Chelsea have offered Leverkusen the chance to sign one of their summer arrivals, Sarr, on loan for the season.
Havertz has spent his entire career at Bayer Leverkusen, contributing an impressive 36 goals and 25 assists in just 118 Bundesliga appearances since making his debut in October 2016.
It is a major coup for Chelsea to secure the signing of Havertz, who had attracted interest from some of the biggest clubs in Europe.
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 has proven pedigree in one of the best leagues in Europe, he plays for the German national side and 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."
German football expert Raphael Honigstein says Havertz will "dominate" Germany's national team over the next 10 years.
"He has work to do and has things to prove because he's only just turned 21, but he's an outstanding talent, there's absolutely no doubt about that. He's in a position where he could dominate the German national team over the next decade, depending on his position," he told the Transfer Talk podcast.
"Will he play in the No 10 role and become the new Mesut Ozil or will he settle a bit deeper and become the new Toni Kroos? He's got the ability to play almost anywhere in front of the defence.
"If you look at the unique combination he has of technical ability and eye for a pass, but also having the ability to score and create goals himself, and his runs to be good in the air, I think the best way to sum it up is that he's a cross between Mesut Ozil and Michael Ballack."
In conversation with Kai Havertz's former coach, Adam Bate traces the player's journey from his breakthrough season to the superstar of today, identifying the qualities that make him so special.
Summer transfer window - key dates and times
The summer transfer window will run for 10 weeks from July 27 and close at 11pm on October 5.
A domestic-only window for trades between the Premier League and EFL then runs from October 5 and closes on Friday, October 16 at 5pm. Follow all the news and analysis on Sky Sports News and across Sky Sports' digital platforms, including with our dedicated Transfer Centre blog.