Norwich will be play at City tomorrow.
Hughton said: "I have to say I was very, very surprised.
"From what I have heard and from what I saw Mancini seemed to have brought some stability to the club. He had won trophies and so I was sure he was there for the long haul.
"That's why his departure was such a surprise."
The last nail in the City manager's coffin was the shock FA Cup Final defeat to Wigan.
And Hughton admitted: "I didn't think they would win the FA Cup comfortably but I honestly thought they would win it."