N'Golo Kante claimed the opportunity to work with new Chelsea manager "was too good to turn down" after completing his £30m transfer to Stamford Bridge from Leicester.
The French midfielder has signed a five-year contract with Chelsea for a bumper contract thought to be worth £150,000 a week.
Chelsea targeted the 25-year-old after an impressive debut season in England in which he played a crucial role in Leicester's title triumph and was named in the Premier League team of the year.
Despite missing out on the opportunity to play in the Champions League with the Foxes next season, Kante said the move to London was "a dream come true".
"I am so happy to have signed for one of the biggest clubs in Europe," he said.
"It's a dream come true for me. The opportunity to work with Antonio Conte, a brilliant coach, and some of the best players in the world was simply too good to turn down.
"My first season in English football was very special and now I hope to go on to achieve even more during my time as a Chelsea player. I am looking forward to meeting up with my new team mates and helping the club achieve a lot of success."
Kante marks Chelsea's second significant acquisition of the summer, following the arrival of Belgian striker Michy Batshuayi for £33m.
Chelsea technical director Michael Emenalo said Kante would be a "perfect fit" for Conte's style of play.
"For a player of his age he has already built up a wealth of experience and his exceptional quality will without doubt be a great addition to the team," said the Nigerian.