After seven years at Stamford Bridge, Brazilian winger Willian will don the red and white shirt of his new club, Arsenal.
He is the latest in a relatively short list of players who moved from Chelsea to their fierce rivals, with only eight players making this particular move.
Before the swap deal involving William Gallas and Ashley Cole in 2006, only two players had ever made a direct move from Chelsea to Arsenal.
A number of players have quite successfully played for both at various points such as Cesc Fabregas, Tommy Lawton and current Blues striker Olivier Giroud, but few have made a success of the seven mile trip to North London from Chelsea.
Here's VAVEL's take on the most successful.
5. Yossi Benayoun, 2011 (loan)
In honesty, anybody could have been bottom of this list.
The Israeli wins out simply through being more effective than the likes of Lassana Diarra - sold after only five months at the Gunners - and Bill Dickson who (after signing from Chelsea in 1953) made only 29 league appearances in three years before being moved on to Mansfield Town.
Benayoun did chip in with some good performances, most notably in a 5-2 win over Tottenham Hotspur in the North London derby.
Not a terrible loan spell.
4. David Luiz, 2019.
Hear us out.
It's true, Luiz's form has been questionable since he made his Arsenal debut, especially when he was sent off in his first return to Stamford Bridge since leaving the Blues.
However his season ended with an excellent performance and more importantly, silverware at the detriment of his previous employers.
3. Petr Cech, 2015
Arguably Blues' greatest ever goalkeeper, many of the Chelsea faithful were disappointed when Cech made the switch to London.
However the move was a shrewd one, as one of Chelsea's 'Munich Heroes' was no longer getting into the side.
He moved to Arsenal in 2015 for a fee of around £10 million and quickly established himself as the club's number one.
A few mistakes hindered his time at Arsenal, but most fans of the Gunners were pleased with Cech's demeanour and professionalism and he eventually earned himself the captaincy.
His career ended in the 4-1 defeat in the 2019 Europa League Final to Chelsea.
2. William Gallas, 2006.
An unpopular figure now since leaving the Gunners for Spurs in 2010, but Gallas originally offered some consolation to fans reeling from the loss of Ashley Cole.
The Frenchman - as well as a fee of £5 million - was offered for Cole and was eventually accepted. However he left in bitter circumstances after Chelsea claimed that Gallas said he would 'deliberately score own goals' in order to force a move, a claim the player denied.
Gallas, named captain the following year, gained revenge on Chelsea when he scored the only goal in a 1-0 victory at the Emirates.
1. George Graham, 1966.
A genuine Arsenal legend, Graham is best known for his time in charge of the club from 1986-95 where he guided them to silverware including two league titles and an FA Cup.
It was as a player that Graham learned the meaning of success. Part of the league and cup double winning side of 1971, the striker turned midfielder is officially named in the top 50 of Arsenal's greatest ever players.
An easy choice for the top of this list.