The midfielder has finally completed his move to the Ligue 1 strugglers on a three-and-a-half year deal.
Cesc Fabregas is officially a Monaco player, with the transfer going through on Friday night following a week of hold-up.
Fabregas made a tearful farewell to Chelsea fans in Saturday's 2-0 FA Cup win at home against Nottingham Forest, where he had a penalty saved.
The 2010 World Cup victor has penned a three-year deal with Monaco, who has been struggling in the French top flight this season.
The club put up a lengthy farewell message on their website highlighting the ex-Barcelona star's achievements in four-and-a-half years at Stamford Bridge.
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"It is a great pleasure to join AS Monaco, [it is] a new project for me", said Fabregas. "I'm here to help the team and I'm impatient to start".
Fabregas scored 22 goals for the London club in 198 appearances. "We have a big game against Marseille on Sunday, I'm very excited".
"The group is quality with young players and a young coach".
Fabregas' departure will now hasten Sarri's need to find a replacement, with the Blues working on deals to sign Cagliari's Nicolo Barella and Zenit St. Petersburg's Leandro Paredes, though there has been no final decision in terms of what kind of player will be brought in to replace the ex-Arsenal man.
Further title success came in the 2016/17 season before he lifted the FA Cup for the first time last season.