Arsenal on Wednesday signed German attacking midfielder Kai Havertz from Chelsea on a "long-term contract".
Neither club disclosed a fee but British media said Arsenal were paying Chelsea 65 million pounds or 75 million euros.
He is Arsenal's first signing of the summer but the British press reported the club had agreed a 105 million-pound fee for West Ham's England midfielder Declan Rice.
Havertz joined Chelsea in 2020 from Bayer Leverkusen. He made 139 appearances in three seasons, scoring 32 times, including the only goal in the 2021 UEFA Champions League final victory over Manchester City.
Arsenal were runners up in the Premier League last season while Chelsea, rebuilding their squad, were 12th.
"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," Havertz told the Arsenal web site.
"The aim is to win trophies and I'm going to give everything to do that."
He posted a farewell message to Chelsea on social media.
He said he was writing "with a heavy heart...saying goodbye to the club that has become my second home, and to the incredible fans who have supported me throughout this amazing journey."
Arsenal boss Mikel Arteta said: "Kai is a player of top quality. He has great versatility and is an intelligent player. He will bring a huge amount of extra strength to our midfield and variety to our play."
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