The attacking midfielder, the younger brother of Eden, signed for the Hungarian club last summer.
The 22-year-old scored four goals in 35 appearances and becomes the third Hazard to sign for Chelsea after older brothers Eden and Thorgan.
Chelsea announced the capture of Hazard today and revealed he will go straight into their development squad ahead of their next match on September 9th after the international break.
Chelsea’s official website reports that Kylian Hazard began his football career with White Star Brussels in Belgium before moving on to Zulte-Waregem. In 2015 he moved to Hungary to join Ujpest, where he went on to play 42 times.
He becomes the third Hazard brother to play for Chelsea after Thorgan Hazard played for the club between 2012 and 2015 before leaving to join Borussia Monchengladbach.
Meanwhile, Thibaut Courtois has said Eden Hazard is the only person who should decide when he makes his comeback after recovering from a broken ankle.
The former Premier League player of the year is yet to make an appearance this season as he recovers from a broken ankle but that has not stopped Belgium calling him up for their upcoming World Cup qualifiers.