The Brazilian centre-half signed a new contract with the Blues in 2019 but rumours of a falling out behind the scenes led to the 32-year-old to force a move away.
Luiz is not the only player to have appeared in a Chelsea and Arsenal shirt and follows suit of Chelsea Technical Director Petr Cech who left for the Gunners in 2015.
Here are ten players to have played in the Blue and Red.
Luiz joined Chelsea in the January 2011 transfer window for £22.5million from Benfica and made 133 appearances scoring 12 goals. The Brazilian defender enjoyed great success in his initial period at Chelsea winning the Champions League, Europa League and FA Cup.
In 2014 he swapped Stamford Bridge for Le Parc de Princes in a whopping £45million deal. After only two years in Paris he returned to South West London on deadline day.
Luiz then became a key piece in Antonio Conte's puzzle the Italian lifted the Premier League in his first season. The middle man of a back three complemented by Cesar Azpilicueta and Antonio Rudiger lifted a Premier League and the Brazilian’s second FA Cup.
Olivier Giroud became a Blue in the January 2018 transfer window with Conte on the prowl for another striker to add to his armoury. £15million proved to be a bargain scoring big goals in big games as well as operating as an influential target man.
The French hitman has gone on to make 63 appearances for Chelsea and playing a part in 31 goals. While at Chelsea, the 32-year-old has won the Europa League beating former club Arsenal in the final and the FA Cup.
Cech joined Chelsea in 2004 from French outfit Stade Rennais for just under £12million. The goalkeeper was one of many high-profile signings that was made by Jose Mourinho such as Didier Drogba, Paulo Ferreira, Ricardo Carvalho, Arjen Robben and Tiago.
The four-time Premier League winner was regarded as was one of the best goalkeepers in the world winning Chelsea Player of the Year seven times along with many other honours.
Chelsea’s new Technical Director played 494 times in a Chelsea shirt keeping 228 clean sheets and averaged 2.12 points a game. A much reliable goalkeeper between the sticks proved vital in the club’s mission for the Champions League trophy.
Robben’s second half penalty. Saved. Cech played an integral part in Chelsea’s famous win at the Allianz Arena over Bayern Munich. Two saves in the penalty shootout later and it was down to Drogba to seal the tie. We all know what happens next.
Cesc Fabregas joined Chelsea from Barcelona in 2014 in search for a second stab at winning the Premier League and in joining the Blues he inevitably did. The 32-year-old won the Premier League twice, the Europa League and a second FA Cup.
In his first season under Jose Mourinho at the Bridge, he appeared 47 times scoring five goals and providing 24 assists. A fairy-tale first season landed the Premier League in his trophy cabinet.
Unfortunately for Fabregas and Chelsea, the following season failed to match expectations with the sacking of Mourinho.
However, Conte was appointed ahead of the 2017/18 season and injected new life into the club handing the Spaniard his second league title in England.
Another ex-Arsenal player who found greater success and silverware at Chelsea.
Ashley Cole joined Chelsea from Arsenal in 2006 for just under £7million and went on to enjoy an eight-year spell at the club winning the Premier League, Champions League, four FA Cups, two Community Shields, the League Cup and the Europa League.
The ex-England international featured 338 times for Chelsea playing a hand in 45 goals averaging 86 minutes a game. A leader and warrior for the club who also captained the side when called upon.
William Gallas became a Blue in 2001 having signed from Marseille in a deal worth £8million. The Frenchman went on to make 222 appearances for Chelsea winning the Premier League on two occasions, the League Cup and the Community Shield.
In 2006 the now 41-year-old left for the Emirates and became their infamous number-ten. The ex-Chelsea defender struggled for minutes in the Premier League with the Gunners and soon opted to move down the road to Spurs.
Nicolas Anelka. The French journeyman who played for twelve clubs two of which were Arsenal and Chelsea spells 11 years apart. None the less the controversial French striker joined Arsenal in 1997 from PSG however was soon jetted off to Real Madrid in 1999.
Nine years later Anelka found himself sign for Chelsea from Bolton Wanders in a deal worth £16million. He appeared 184 times for Chelsea (more than any other club) scoring 59 goals.
An imperative player for Chelsea and Carlo Ancelotti that made up one of the league’s most deadly strike forces with the likes Didier Drogba, Saloman Kalou and Florent Malouda.
Anelka lifted the Premier League, League Cup and the Community Shield each of the latter two twice.
Emmanuel Petit joined Chelsea in 2001 from Barcelona for £10million before retiring with the club in 2004. The French midfielder spent the latter years of his career with the Blues having spent much of his prime at Arsenal.
The World Cup winner played 72 times for Chelsea but failed to grasp any silverware.
Lassana Diarra enjoyed two seasons with Chelsea after joining from Le Harve for £4million in 2005. The powerful midfielder won the Premier League, FA Cup and the League Cup before joining Arsenal in 2007.
The Frenchman played just 31 times for the Blues over two seasons and struggled for game time in a domestically dominant Chelsea side.
Graham played appeared in a total of 380 games for both Chelsea and Arsenal. The Scottish midfielder was a pivotal player for both sides in the mid-60s and 70s.
Chelsea signed the Scotsman for £5,000 in July 1964 and went on to score 35 goals in 72 games along with winning the League Cup in 1965.
Graham found greater success at Arsenal winning the domestic double in 1970/71. He played 308 times for the Gunners scoring 77 goals.