Chelsea have agreed a fresh six-year deal in principle with Levi Colwill to keep him at Stamford Bridge until at least 2029.
The 20-year-old stands to earn £100,000-a-week on his new contract, which is expected to be finalised soon.
Brighton had been keen on bringing the England Under-21 international back to the south coast after impressing on loan last season.
However, they had bids of £30million and £40m rejected by the Blues, who intend to make Colwill part of their first-team plans for the upcoming campaign.
The youngster is expected to get a fair amount of playing opportunities and will be able to get a head start on his main competition as fellow left-sided centre back Benoit Badiashile remains sidelined by a serious hamstring injury.