While most expected Alexis Sanchez to end up at Manchester City, it was their red neighbours who eventually agreed to stump up the cash for the Chilean forward in one of the most reported transfer sagas of all time.
It's far from the first time a player has moved between north London and Manchester. Here's a look back at some of the most famous deals done between Arsenal and the two Mancunian sides.
1. Emmanuel Adebayor
The Togolese journeyman never spent more than three seasons with one club. Starting his senior career at Metz in 2001, he went on to play for Monaco, Spurs and Crystal Palace among others and is still going over in the Turkish Super Lig at the age of 33.
In 2009, City began their haul of wantaway Arsenal players as they signed Adebayor as well as Kolo Toure in one month.
The signings were among the first that City's new owners would be making in order to push the club to the very top.
Although Adebayor didn't exactly light the Premier League on fire during his time at the club, scoring only 15 goals in three seasons, it did pave the way for more Arsenal talent to make the switch to City.
2. Gaël Clichy
Gael Clichy was very open about his desire to compete for silverware with City and the full back told the Independent back in 2011: "I joined City because I wanted to win a lot of things."
Clichy won four trophies in five years with City, while parallels have been drawn with former Spurs man Kyle Walker, who was similarly open in his desire for silverware last summer before his £50m move to the Etihad stadium.
3. Danny Welbeck
Up until 2014, Welbeck had spent his life at United, working his way up through the youth teams, punctuated by loan spells, before ending up in United's first team.
Though after a few seasons, he found himself on the bench far too often and the decision was made to move to another club where first team football was more likely.
In came Arsenal, who paid £16m for his services during the final moments of summer 2014's deadline day. After a stint in the first team, yet again Welbeck has found himself more often than not on the bench and may be on the lookout for another club sooner rather than later.
4. Samir Nasri
The City signing of Samir Nasri in 2011 marked the full swing opening of Arsenal's Mancunian exodus.
Nasri was only 24 when the transfer was made and had already scored 27 goals for the club from midfield. Though to the dismay of Arsenal's fanbase, it was widely regarded that the club's desire to cash in on the player was too great and the deal was done for £25m.
The Frenchman didn't have the best of times in Manchester, scoring the same amount of goals he did for Arsenal, though in 51 more games.
5. Mikaël Silvestre
Another example of a United player moving to Arsenal with the hope of more first team football. Silvestre was coming out of his best years as a footballer and could no longer make the first team under Sir Alex Ferguson at Old Trafford.
At the age of 30, the French connection with Arsenal was too hard to turn down as the defender chose to join Wenger's team after offers from Bordeaux and Man City.
The transfer made Silvestre the first player to transfer directly between Manchester United and Arsenal since Viv Anderson went the other way in 1987.
6. Robin van Persie
The signing that led Arsène Wenger to claim that no more players would be sold to United.
Robin Van Persie's move to United was controversial to say the least and he has remained a persona non grata with many Arsenal fans.
However, the Dutchman became an instant hit at United. He was instrumental in the club's Premier League triumph in his debut season under Ferguson and won the club's player of the year for the 2012/13 season - the last time United won the Premier League title.
- 90Min