Lille's Belgian international playmaker Eden Hazard snubs Manchester United/City for the Blues, for reported fee of 40million euros (50.14million US)
The fee is reported to be 40million euros with Hazard signing a five year contract and breaks the record for a Belgian footballer's transfer with Marouane Fellaini's to Everton of 20million in 2008 being the previous mark.
He will also earn a reported 550,000 euros a month.
The 21-year-old - who was voted Ligue 1 Players' Player of the Year for the second successive year recently - had previously said he would definitely sign for one of the Manchester clubs without specifying which one.
However, Chelsea's penalty shootout win over Bayern Munich in the Champions League had he admitted at the time made him hesitate as to his choice - speculation he ended on Monday even though the transfer window doesn't officially open till June 13.
"I'm signing for the Champion's League winner," he tweeted.
Hazard, capped 27 times and scorer of two goals, was inspirational when Lille won the domestic double in 2011 and though they failed to defend their titles this season he nonetheless enjoyed a successful season, scoring 17 goals and providing 15 assists.
Hazard is due to play against several of his new team-mates in Saturday's friendly with England at Wembley.
New Belgian national coach Marc Wilmots said that no-one should expect too much else to be said on his reasons for choosing Chelsea for the moment.
"When he has revealed via his tweet, his destination, he will remain silent until his new employer asks him to explain his choice. Don't hope for much more in the next dozen days or so," Wilmots said at a press conference.
Click on the photos above to see more pictures of the Belgian midfielder Eden Hazard.