Kai Havertz to Arsenal as happened, as the 24-year-old has signed a "long-term deal" at Emirates Stadium, three years after joining the Blues from Bayer Leverkusen for £71m.
The fee for Havertz, who scored nine goals for the Blues last season, could rise with add-ons.
Havertz has scored 19 goals in 91 Premier League appearances and hit the winner in the 2021 Champions League final against Manchester City.
He moves across London as Mikel Arteta looks to strengthen his Arsenal side following qualification for the Champions League after a six-year absence.
In a statement on his social media channels, Kai Havertz to Arsenal happened as he said it was "with a heavy heart" that he was saying goodbye to Chelsea's fans.
"A big thank you for all your support, we achieved a dream of winning the Champions League together," he added.
Speaking on the Arsenal website after his transfer had been announced, Havertz said his aim was to "win trophies" with his new club.
The high point of Havertz' Chelsea career is undeniably his match-winning goal in the 2021 Champions League final against Manchester City that delivered the second European Cup in the team's history.
"It's super exciting for me to be joining this amazing club and to be part of the Arsenal family," Havertz said. "This club has such a big history, and I hope we can achieve lots of things.
"The mentality in the Arsenal squad is very high and you can feel that. That was one of the reasons why it has been so hard to play against Arsenal recently.
"The aim is to win trophies and I'm going to give everything to do that for the supporters and everyone at the club. I'm now looking forward to meeting all the players and the staff when we come back for preseason."
ESPN reported last week that Havertz had informed Chelsea that he had no interest in signing a new contract with the club — he will likely make his Arsenal debut against Nottingham Forest on Aug. 12.
Havertz' departure from Chelsea comes amid wholesale changes at the west London club as owners Clearlake Capital and Todd Boehly look to trim the size of their squad ahead of the arrival of new head coach, Mauricio Pochettino.
N'Golo Kante, Kalidou Koulibally and Edouard Mendy have already left Chelsea to join Saudi Pro League clubs, while Hakim Ziyech, Christian Pulisic and Mason Mount are among those to have also been linked with moves away.