From the official site:
Manchester City is deeply saddened to hear that Mike Doyle has passed away aged 64.
Mike was an integral part of the City team that won the League title, FA Cup, European Cup Winners' Cup and the League Cup between 1968 and 1970. He also captained the side that won the League Cup once again in 1976.
He played over 550 times for the Blues between 1962 and 1978, and as well as being an imposing presence in defence, Mike had a handy knack of popping up to grab the odd vital goal.
Everyone at the club extends their deepest condolences to Mike's family.
A round-up of some of the tributes and memories to Doyle:
The MEN has a picture round-up here.
Who Ate All The Pies has a look back at his career (with some great archive photos) here.
Mike Summerbee: "Mike was somebody you always wanted alongside you when the going got tough. He was a great footballer, a magnificent servant to this club, and he was also a nice bloke into the bargain."
The official site now has an obituary up.