Maurizio Sarri has left Chelsea to become manager of Serie A champions Juventus on a three-year deal.
Sarri, who joined the Blues from Napoli in July 2018, led them to third in the Premier League and won the Europa League in his one season in charge.
It is understood compensation in excess of £5m has been agreed between the two clubs for the 60-year-old.
Sarri will replace fellow Italian Massimiliano Allegri, who left Juventus at the end of last season.
"In talks we had following the Europa League final, Maurizio made it clear how strongly he desired to return to his native country, explaining that his reasons for wanting to return to work in Italy were significant," said Chelsea director Marina Granovskaia.
"He also believed it important to be nearer his family, and for the well-being of his elderly parents he felt he needed to live closer to them at this point."
Sarri signed a three-year deal last July but now becomes the ninth full-time manager to leave Chelsea under Roman Abramovich, who bought the club in 2003.
Derby boss and former Chelsea midfielder Frank Lampard has been linked with taking over from Sarri but the Blues are yet to make contact with the Rams.
The Championship club are keen to extend Lampard's deal - which has two years left - and have opened talks with the 40-year-old.
Chelsea are unable to sign any players after being given a two-window transfer ban by world governing body Fifa - a decision they are appealing against at the Court of Arbitration for Sport.
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'He has gone, Chelsea will move on'
Former Chelsea winger Pat Nevin felt Sarri was capable of building on his debut season, but accepts many fans will be indifferent about his departure.
"I don't think they are absolutely devastated," he said. "It is one of those ones where some people wanted him to stay and some wanted him to go. I am one of the ones who would have been delighted had he stayed.
"However, great Chelsea managers come along like 42 busses every two minutes - there will be another one. He has gone. He has done a brilliant job and probably would have done even better next season.
"In the current situation it doesn't matter who is manager because you are not going to catch Manchester City or Liverpool at the moment. Top four? That would be enough but even that is a big, big call without Eden Hazard."
'Sarri not the right man for Juventus'
Under Allegri, Juventus won five Serie A titles, four Coppa Italias and finished runners-up in the Champions League twice.
"Sarri does not strike me as the right man for Juventus," said European football expert Mina Rzouki. "They also did not seem to think so a few years ago when there was potential that Allegri would leave and Sarri was doing wonders at Napoli at the time.
"For many reasons Sarri is a man who prefers the beauty of football, sometimes over even the wins.
"Allegri is a winner, but his style does not necessarily bring out the best of the players and it all seemed a little dull and stale at the end.
"For Sarri, a man who has worked his way up from being a banker, this is a huge achievement. He is at the helm of Juventus - the richest and most successful side in Italy. Whether or not this is the right fit we will find out."
Sarri's ups and downs at Chelsea
Sarri succeeded compatriot Antonio Conte, who was sacked after two seasons in charge despite winning the Premier League and FA Cup in 2017.
After earning glowing references for his tactics at Napoli, Sarri looked to have effectively introduced 'Sarri-ball' to his new players as Chelsea started their Premier League campaign with a 12-game unbeaten streak.
But they were out of title contention after losing three out of four Premier League games from January to February, including a 6-0 defeat at eventual champions Manchester City, which saw them slip to sixth in the table.
Chelsea then lost 2-0 at home to Manchester United in the FA Cup, when fans booed Sarri's substitutions and joined in when the visiting supporters sang "you're getting sacked in the morning".
Sarri alienated some supporters by moving N'Golo Kante, regarded as one of the best players in the world in a deep-lying midfield role, to the right of a three-man midfield to accommodate Jorginho.
There was repeated speculation about Sarri's position and this increased when goalkeeper Kepa Arrizabalaga challenged his authority by refusing to be substituted in the Carabao Cup final at Wembley, shortly before Chelsea were beaten in a penalty shootout by City.
Of the 19 matches played after losing to City at Wembley, his side lost just two, as they won their first European trophy since securing the Europa League in 2012-13.
They also held off the challenge of Tottenham, Arsenal and Manchester United to finish third in the league and clinch Champions League qualification.
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Chelsea in the transfer market under Sarri
Under Sarri, last summer Chelsea spent a record £71m on Arrizabalaga, as well as £50m to reunite him with Jorginho, the former Napoli midfielder who struggled in his first season in England.
In January, Juventus striker Gonzalo Higuain joined until the end of the season, again reuniting Sarri with a former player, while £60m striker Alvaro Morata went to Atletico Madrid on loan.
Bayern Munich made a £35m bid for Callum Hudson-Odoi, aiming to capitalise on a lack of game time for the 18-year-old, with England manager Gareth Southgate seemingly showing more faith in the youngster than Sarri.
However, the winger did not leave in January and, after getting more first-team football as the campaign progressed, ruptured his Achilles tendon in April.