Brazil forward Joao Pedro has joined Chelsea from Brighton to continue the London giants' lavish spending under American owners Todd Boehly and Clearlake Capital.
Joao Pedro cost a reported $A125 million and has signed a contract through to 2033.
"Everyone knows this is a big club with a great history," Joao Pedro said. "They had brilliant players in the past and have brilliant players now. So I am excited to join and you know when you are a Chelsea player you must think one thing - win."
He has joined up with Chelsea's squad at the Club World Cup in the United States and is eligible to play in Friday's quarter-final against Palmeiras.
Joao Pedro is Chelsea's fifth major signing this offseason after previous deals for Liam Delap, Dario Essugo, Kendry Paez and Mamadou Sarr.
Under Boehly and Clearlake, the six-time English Premier League champions have spent well in excess of $A1.53 billion on transfers, including British record fess for Enzo Fernandez and Moises Caicedo.
Joao Pedro's arrival comes as Chelsea prepares for a return to the Champions League after a two-year absence.
Bayer Leverkusen have signed defender Jarell Quansah from English champions Liverpool in a £35 million deal.
The 22-year-old centre-back has joined the German Bundesliga club on a five-year contract.
Quansah was part of the England side who won the European Under-21 Championship by beating Germany in the final on Saturday.
His move is the third deal between the clubs this summer after Liverpool signed midfielder Florian Wirtz and defender Jeremie Frimpong.