Defender Levi Colwill has signed a new six-year deal with Chelsea, with an option for a further year.
The England Under-21 international helped Brighton qualify for the Europa League last season, making 17 Premier League appearances while on loan at the club.
"It's always been an easy decision," said Colwill.
"'As I've grown up, all I've known is Chelsea. I've spoken with the manager [Mauricio Pochettino] and he's given me reassurance, that trust I needed.
"He's spoken with me not just as a player but a person. It's made a big difference."
Colwill joined Chelsea at the age of eight, progressing through the Blues youth teams before being loaned to Huddersfield in 2021/22, where he made 29 Championship appearances and helped the club reach the play-off final.