The Blues made their controversial move to bring the Spanish international back to London, three years after the former Arsenal captain left the capital to move back to boyhood club Barcelona. The 27-year-old had failed to impress on a consistent basis upon his return to Catalunya, and was promptly sold this summer as new boss Luis Enrique looks to rebuild the team at the Camp Nou.
With a £27m asking price on the midfielder's head, former club Arsenal as well as Premier League rivals Manchester United were both linked with swoops to bring him back to England, but it was Chelsea who made the shock move to sign him, completing the deal on Thursday.
A versatile player who can play in front of the back four, as a box-to-box midfielder or even further forward as a false centre forward, there have been plenty of questions about how Fabregas will be used at Chelsea, but manager Mourinho has outlined how he differs from the current midfield options at the club.
"Cesc is a great player who brings something new to our team," said Mourinho. "He's different to Matic, Ramires and Oscar. We'll have a very complete midfield with him in the side. In signing Cesc I'd wanted to bring in a midfielder with a certain profile and now I have just that," he added.
It seems most likely that Fabregas will be deployed alongside Nemanja Matic in the base of the Chelsea midfield, with Matic holding, allowing Fabregas to get forward and support the likes of Eden Hazard, Willian and Oscar in attack.
The relationship between Fabregas and Mourinho hasn't always been great after spats during their times at Barcelona and Real Madrid respectively, but the Chelsea boss says it won't be an issue.
"There's no problem. We spoke and got everything out in the first five minutes. He knows what I think and everything is very clear," said Mourinho.
Where should Fabregas be used at Chelsea?