"I am really looking forward to it now. Manchester City is a massive club and there was no saying no," Thatcher told the Man City official website.
"Now I just want to get on with it, do my best, and hold down a first team place."
He added: "Until I signed for Leicester last year I had played all my football in London but it has not been a problem for me moving north.
"I played in the new stadium last year in the League game with Leicester and the City of Manchester Stadium is a fantastic place to play football."
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