Brazil midfielder Willian has joined Arsenal on a three-year deal after leaving Chelsea expired on a free transfer.
The 32-year-old rejected the offer of extending with Blues because they were unwilling to match what the package the Gunners had on offer.
He will wear the number 12 shirt at the Emirates.
“I believe he’s a player that can really make a difference for us,” said Arsenal boss Mikel Arteta.
“We had a clear intention to strengthen in the attacking midfielder and the winger positions.”
Willian made 339 appearances, scored 63 goals and made 56 assists for Chelsea after signing from Russian side Anzhi Makhachkala for £30m in 2013.
Throughout his seven years at Chelsea, he won two Premier League titles, an FA Cup and the Europa League.
“He is a player that gives us a lot of versatility, he can play in three or four different positions,” added Arteta.
“He has the experience of everything in the football world but still has the ambition to come here and contribute to bring the club where it belongs.
“I have been really impressed with all the talks I have had with him and how much he wanted to come.”
An established international, Willian has made 70 appearances and has scored nine goals for five-time world champions Brazil, since making his international debut in 2011.
He has represented his country at the 2014 and 2018 World Cups, the 2015 Copa America, the Copa America Centenario, and the 2019 Copa America where he was a key member of the squad that lifted the trophy on home soil.
Technical director Edu said: “I know him very well, since a long time ago because we’ve been working together for the Brazilian national team and of course I was following him because he played for another club.
“He has a lot of fantastic attributes as a person, as a football player of course, his character. I’m 100 per cent sure that everybody in the dressing room, the fans, myself and Mikel will enjoy having Willian in our side.“