Arsenal have completed the signing of Brazil defender David Luiz from Chelsea in an £8m deal.
Luiz, 32, joins the Gunners on a two-year contract, with the deal following Arsenal's £25m deadline day purchase of Celtic left-back Kieran Tierney, 22.
Arsenal manager Unai Emery said Luiz brings "huge experience" and "adds to our defensive strength".
Luiz takes Emery's summer spending over £130m after deals for Nicolas Pepe, William Saliba and Gabriel Martinelli.
The Gunners are set to recoup around £34m for winger Alex Iwobi as he is set to complete a deadline day move to Everton and they have also sold Krystian Bielik, Laurent Koscielny, Carl Jenkinson, David Ospina and Takuma Asano during the summer window.
The departures take their summer transfer income to about £55m.
Having signed for Chelsea from Benfica in a £21m deal in January 2011, Luiz joined Paris St-Germain for £40m in June 2014 before returning to Stamford Bridge in August 2016 for £34m.
He spent six and a half years at Chelsea in all and won the league title, two FA Cups, the Champions League and the Europa League twice.
He signed a two-year deal with Chelsea in May and his departure comes five weeks after Frank Lampard returned to Stamford Bridge to manage his former club.
Chelsea are banned from signing players until the end of January 2020 following an investigation into their signing of foreign under-18 players.
With Gary Cahill, who has since joined Crystal Palace, released at the end of last season, Chelsea's options at centre-back include Germany's Antonio Rudiger, Kurt Zouma, who was on loan at Everton last season, and Denmark's Andreas Christensen.
Tierney meanwhile said it proved a "hard decision to leave a club that you love so much" as he completed his move from Celtic for a Scottish record fee.
The Scotland international said he was "sorry" as he could not repay Celtic's fans for their support "in any way possible".