The £65 million deal is City’s third big deal of the transfer window after the arrivals of Nathan Ake and Ferran Torres.
Nicolas Otamendi will go the other way and join Benfica for £13.7m.
While announcing the Dias signing on their official website, City made two rather embarrassing mistakes.
The first was including a link telling fans they can ask new signing Kalidou Koulibaly a question, while the second link gave fans the ability to win a signed Koulibaly shirt.
Just a simple mistake? A sign of a failed signing? These are questions fans will ask but likely never be given answers to.