Conor Gallagher signed a new contract with Chelsea before heading to Charlton Athletic on-loan this season.
His new Chelsea contract commits him to his boyhood club until at least 2022 and he will now link up with Lee Bowyer's newly promoted Addicks in the Championship for his first experience of senior football on loan.
Bowyer said, “He's an exciting young player. He can put his foot in, create, score and has a bit of everything so I'm over the moon to have him through the door. Clubs like Chelsea recognise what we have done previously with the young midfielders we had last season and this will be no different.
"I'd like to thank them for the part they played in Conor coming to us."
Head of Recruitment Steve Gallen has watched Gallagher regularly for Chelsea's U23s and is very pleased with what the Addicks are getting.
He explained: “It's something that's been rumbling along for a few weeks and there were a few clubs in for Conor, as well, so I'm doubly pleased to beat them to his signature and do it in time for the first game of the season. His attitude is excellent, he likes to run, tackle and get up and down the pitch and his all-round midfield game makes him a very good addition for us."