Wesley Fofana completed his £70 million move from Leicester to Chelsea and aimed a parting dig at former boss Brendan Rodgers.
The defender has signed a seven-year contract at Stamford Bridge, the Blues confirmed on Wednesday.
Fofana joins Kalidou Koulibaly and Marc Cucurella as defensive reinforcements for boss Thomas Tuchel this summer.
It ends a transfer saga which Rodgers admitted had helped to derail his side’s Premier League season already with the Foxes winless and bottom of the table after four games.
Fofana, who has recovered from a serious broken leg he suffered in pre-season last year, had pushed to join Tuchel’s side and failed to turn up for training with the Foxes earlier this month.
But the 21-year-old defended himself and thanked Rodgers for his support, even if he questioned some of the comments from the Foxes while he was there.
He wrote on Instagram: “During these two seasons here, I have probably experienced the most intense moments of my young football career. I have grown as a player but also as a man.
“Thank you to you, Foxes fan(s), for your kindness and your constant support, even in the moments you were led to believe I didn’t respect the club. I will never forget how we vibrated, exulted or cried, together… I will never forget you.
“I chose not to communicate during this transfer window despite all the criticism and all the often false and misleading comments, even when they were coming from the club.
“I understood and I learned. I didn’t want to damage the image of the institution and I chose to take it rather than answer. I thank Top (Srivaddhanaprabha, chairman) for his understanding, thanks to the managers, to the coach who has always appreciated me, even if he chose to expose me a lot lately… I got it coach.
“Thanks to the staff for their trust, their advice and of course, their support during my injury and my recovery period.
“There were ups and downs but I never cheated, you can be sure of that. Thank you to all the people who work here everyday, you are the soul of this club!”
Saint Etienne are also due a slice of the fee as part of the deal which saw Fofana move from France to Leicester in 2020.
He helped the Foxes win the FA Cup, for the first time in their history, in 2021 and made 52 appearances for the club.
Chelsea chairman Todd Boehly said: “Wesley is a hugely promising defender who has already proven his quality in the Premier League at a young age.
“We are delighted we were able to bring one of Europe’s most exciting talents to Chelsea and further strengthen that area of our squad, both for this season and many more to come.”