Chelsea completed the signing of Ecuadorian midfielder Moises Caicedo for a reported Premier League record fee of up to £115 million ($146 million) on Monday.
The Blues said the 21-year-old has agreed an eight-year contract at Stamford Bridge, with a club option for a further year, after Chelsea beat off Liverpool for his signature.
It is the second time Chelsea have broken the British transfer record in seven months after spending £107 million on Enzo Fernandez in January.
Liverpool had a £110 million bid accepted on Friday after Brighton had set a deadline for bids.
But Caicedo turned down the opportunity to join the Reds to pursue a move to the Blues.
"I am so happy to join Chelsea!" Caicedo said in a club statement.
"I am so excited to be here at this big club and I didn't have to think twice when Chelsea called me, I just knew I wanted to sign for the club.
"It's a dream come true to be here and I can't wait to get started with the team."
Chelsea will reportedly pay an initial £100 million with a further £15 million due in performance-related bonuses.
The deal represents another huge profit for Brighton, who signed Caicedo from Ecuadorian side Independiente del Valle for just £4 million in 2021.
"Chelsea are getting one of the top midfielders in the world," said Brighton's technical director David Weir.
"Moises has been one of our exceptional players over the past 18 months."
Chelsea have spent close to £900 million on players in just three transfer windows since a takeover fronted by LA Dodgers co-owner Todd Boehly and private equity group Clearlake Capital.
However, they slumped to 12th in the Premier League last season -- their lowest finish since 1994.
New manager Mauricio Pochettino's reign got off to a promising start in a 1-1 draw with Liverpool on Sunday.
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