Barcelona announced the news on Thursday.
That's a horrifying thought for Arsenal fans, and it's one that will become tangible when Fabregas pulls on a Chelsea shirt against the club that nurtured him and rejected the chance to take him back for a reduced price.
It's a decision Arsenal will almost certainly regret.
There is simply no better value that Arsenal could have had in the transfer market this summer. Of course, the club still needs an elite striker, a right-back, a back-up goalkeeper and probably another centre-back. But Fabregas would not have broken the bank at all.
Metro report that Fabregas only cost Chelsea £27 million, an absolute pittance for a player of his quality. Every time he has been sold, the selling club has received much less than what he was worth—when he left Barcelona at the age of 16, when Arsenal sold him for an initial payment of £25 million in 2011 and especially now.
Fabregas is 27 years old and is in the prime of his career. He is not only a supremely talented and imaginative creator, but a clinical finisher as well. He had a knack for finding the net at Arsenal and honed his final touch even further when deployed in more advanced attacking positions at Barca.
Perhaps Arsenal do not need Fabregas' skill set now as much as they did a season or two ago. But a team that often had a lot of trouble in front of goal could really use a midfielder whose specialty is putting the ball in the back of the net.
Of course, Arsenal already have one of the best attacking midfielders in the world in Mesut Ozil and several other elite options such as Aaron Ramsey, Jack Wilshere and Santi Cazorla. Why add to the one area of the squad jam-packed with depth?
Barcelona were willing to let Fabregas go on the cheap. The Gunners also had the option of using the buyback clause in Fabregas' contract to block any other club from nabbing a fantastic player at a cut rate.
It is foolish not to do so. By purchasing Fabregas, Arsenal would not only have enriched themselves on the pitch and bought insurance against future injury crises, but also prevented their direct title rivals from becoming significantly stronger.
Moreover, this would have been a signal of intent to other elite clubs: The Gunners would effectively have been stating that they are now major players in the transfer market, capable of influencing the business of multiple heavyweight clubs all by themselves.
Chelsea's midfield and attack is now an absolute force to be reckoned with. With Nemanja Matic as the enforcer and Fabregas as the creator for Eden Hazard, Diego Costa, Andre Schurrle, et. al., the Blues will be ruthless. No more of the bus parking for which Jose Mourinho is so infamous.
Arsenal will surely be remembering this when they are forced to endue their seasonal injury crisis and Arsene Wenger has absolutely no ability to rotate the midfield.
Moreover, many of the Gunners' present options in the middle of the pitch are fragile and aging. Mikel Arteta is rapidly slowing down, Tomas Rosicky is 33, Abou Diaby is Abou Diaby and Cazorla is coming off a very underwhelming campaign.
Importantly, Ozil has not proven himself for an entire season, and Ramsey and Wilshere have each had prolonged spells on the sidelines due to injury.
This is a very pessimistic analysis, but Wenger is an utter fool if he did not consider the worst possible eventuality before deciding to let Fabregas sign for a direct title rival.
Is there really any better insurance that Arsenal could have bought for £27 million?
Even if the club had taken Fabregas back, they still would have had tens of millions of pounds left in their transfer kitty to purchase that fabled striker, a right-back and a cheap back-up goalkeeper.
Perhaps Fabregas will burn out at Chelsea or Arsenal will have a truly historic summer and drastically improve their squad so that they can be genuine title contenders. But this move seems very similar to Robin van Persie's move to Manchester United in 2012, which effectively handed the Red Devils the title.
Wenger had better have a potent Quaalude for Arsenal fans, who are rightly incensed that Fabregas was allowed to join one of their most bitter rivals with what is essentially their explicit consent.