Conte spent two seasons in charge of the Premier League club, leading them to the title in his first year.
The Blues were unable to defend their title, finishing fifth last season and missing out on Champions League.
Conte was relieved of his duties after he conducted training at Cobham for the final time on Thursday morning before saying his goodbyes to players and staff.
Even Andre Villas-Boas, who was dismissed after nine months in 2012, was thanked for his contribution by the club, who even expressed their "disappointment that the relationship" ended prematurely.
Conte's been absent from all social media posts by the club, which has only fuelled rumours that he won't be in charge by the time the Premier League season starts in August.More news: Russian Cargo Ship Makes Fastest-ever Trip to Space Station
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Sarri's got a buyout clause at Napoli rumoured to be in the region of €8 million while Conte will get a hefty severance package as well so the "switch" won't come cheap for the West Londoners.
Sarri will become the 12th manager to take over the reins at Chelsea since Roman Abramovich bought the London club in 2003.
Chelsea believe Conte's behaviour effectively breached the terms of his contract as manager.
The former Juventus boss was one of the managers on Madrid's shortlist after Zinedine Zidane's departure in May but he refused.
However, while present players may have had issues with Conte, former Chelsea legend John Terry, who left after the league title winning campaign had nothing but praise for him.
Two trophies in two seasons but the writing was on the wall.