The Italian, who led City to their first league title since 1968 last season, was sacked earlier this week following a disappointing campaign where they lost their Premier League crown to Manchester United and knocked out of the Champions League at the group stage.
Mancini has always has a good relationship with the fans and in a full-page advert in the Manchester Evening News wrote: "Manchester City Supporters 3 unforgettable years, you will always be in my heart, ciao, Roberto Mancini."
As well as the league title, Mancini won the FA Cup with City in 2011 and Community Shield last summer.