Chelsea have announced that Tiemoue Bakayoko returns to Monaco on loan for the season.
According to GOAL, the loan includes a €42.5m (£38m/$46m) option to buy.
Bakayoko scored three goals and helped Chelsea win the FA Cup final.
He spent last term on loan at AC Milan where he made 42 appearances in all competitions, scoring one goal which came against their city rivals Inter in a 4-3 defeat.
Born in Paris, Bakayoko came through the Rennes academy in the north-west of France and made his senior debut in August 2013, a week after his 19th birthday.
He signed for Monaco the following summer and featured almost 100 appearances for the principality side during his three seasons there, scoring five goals.
In 2016/17 he starred as they unexpectedly beat Paris St-Germain to the title and also reached the last four of the Champions League, knocking out Manchester City and Borussia Dortmund en route. Bakayoko scored the decisive goal in a thrilling two-legged tie against the Premier League side.
He returns to Monaco where he will call Cesc Fabregas a team-mate once again after the season they spent together as Chelsea midfielders.
Monaco are managed by Leonardo Jardim, who Bakayoko played under during his first spell at the club, and are currently 19th in Ligue 1 having lost two and drawn one of their opening three games.