Arsenal have completed the signing of Willian on a three-year contract.
The winger, who spent seven years at Chelsea, had reached the end of his contract at Stamford Bridge.
Willian, 32, wanted a three-year contract to stay at Chelsea but the club were only willing to offer him a two-year deal.
“The time has now come to move on,” Willian wrote in a recent open letter to Chelsea fans.
“I leave with my head held high, safe in the knowledge that I won things here and always did my best in a Chelsea shirt.”
Willian backed out of a proposed move to Tottenham and signed for Chelsea from Russian side Anzhi Makhachkala for £30m in 2013.
He made 339 appearances for the Blues, won two Premier League titles and the Europa League and was twice voted the club’s player of the year.