David Luiz will wear the No 23 shirt after signing for Arsenal in a deal worth £8m.
The Brazilian joins from Chelsea on a permanent contract having pushed for a late move earlier this week.
The 32-year-old defender trained separately from the rest of the first-team squad yesterday having made clear his desire to leave.
A rift between Luiz and Frank Lampard is believed to have emerged during the off-season, with Chelsea happy to sanction the cross-city switch.
Manager Unai Emery said: “David has huge experience and I look forward to working with him again. He is a well known player and adds to our defensive strength.”
Luiz follows Kieran Tierney as Arsenal’s second signing on deadline day.
The Scotland international has signed a five-year deal to move to the Emirates Stadium from Celtic, where he made his breakthrough four years ago and made 170 appearances in a 12-year career with his childhood club.
“I’m a Celtic boy, born and raised,” Tierney said upon his unveiling. “Joined my boyhood club, came up through the ranks and earned my place. Now, I’ve come to London and I want to make some noise.”
