Defender Nedum Onuoha's mum was devastated when she received the message, which was intended for City's football administrator Brian Marwood — and appeared to be sent by the club's chief executive Garry Cook.
Cook has denied to Dr Onuoha that he had ever sent the message — which cruelly ridicules her illness — and has insisted to her that someone broke into his own e-mail system as a practical joke.
But Dr Onuoha, battling an aggressive form of cancer, is not happy with that explanation.
And last night she asked the FA and Premier League to investigate, handing over all her e-mail evidence to both bodies.
Dr Onuoha said: "When I opened up my e-mails and saw the message, it was the worst day of my life, even worse than being diagnosed with cancer.
"I couldn't understand how anybody could behave like that. I'm critically ill.
"I just cried and cried for hours."
Dr Anthonia Onuoha, who acts as Nedum's agent, last night sent official letters of complaint to the FA and Premier League about the e-mail she received during her year-long fight against cancer.
Cook has denied sending the message, explaining his e-mail system was broken into and a full internal inquiry has been launched at City to find the culprit.
The offensive e-mail emerged after Dr Anthonia wrote to City's football administrator, Brian Marwood, about a contract dispute her son was having with the club.
In October last year she e-mailed Marwood explaining that, while her body might be "ravaged with cancer and ongoing chemotherapy" she still had her wits about her to argue Nedum's case.
Two weeks later Dr Anthonia received an e-mail — which appeared to be from Cook and was meant for Marwood — but was instead sent to her.
The e-mail was addressed 'Brian' then said: "Ravaged with it!!......I don't now how you sleep at night. You used to be such a nice man when I worked with you at nike (sic)."
A devastated Dr Anthonia replied to Cook the following day saying: "Thanks very much for your insightful e-mail."
Cook responded, saying he hadn't sent the offending e-mail and that his e-mail account had been hacked while he was on holiday in South Africa for 10 days.
He insisted that, following an internal investigation, he had learned a member of his staff had sent the e-mail to Marwood as a joke.
He told Dr Anthonia: "I cannot and will not condone this unacceptable behaviour. I can confirm Brian did not receive this e-mail and disciplinary action is currently underway regarding one of our employees."
Cook also apologised for "any hurt or embarrassment this may have caused".
Dr Anthonia said: "When I opened up my e-mails and saw the message, it was the worst day of my life, even worse than being diagnosed with cancer.
"I couldn't understand how anybody could behave like that. I just cried and cried for hours.
"I'm critically ill and at that point I was undergoing chemotherapy. I was just so shocked but I couldn't tell Nedum or any of my family because I didn't know how they would react.
"It's incredible that any human being would write this. It's unforgivable and I still cannot believe it.
SunSport revealed yesterday how a vile e-mail was sent from Cook's account to the mother of City defender Nedum Onuoha which mocked her battle against cancer.
City last night confirmed a "board-led review" would begin this morning into the scandal as calls for Cook to resign began to grow.
The e-mail, which carried the message "sent from my iPad", had been intended for City's football administrator Brian Marwood.
But instead it was sent to Nedum's mother Dr Anthonia Onuoha, leaving her deeply distressed and anguished.
Cook later told her he did not send the message, insisting his e-mail account had been hacked into while he was on holiday and that — after an investigation — the culprit was being dealt with.
However, we can reveal that Dr Onuoha has contacted City chairman Khaldoon Al Mubarak saying she refuses to believe Cook's version of events.
We understand she is demanding that Cook admits he sent the offending e-mail and that he apologises for his actions.
Dr Onuoha has also asked the FA to investigate Cook under rule E3 which covers improper conduct.
The FA were still considering their position last night but it is understood they may leave it to City to resolve the matter.
City have issued a statement confirming they will now investigate the scandal.
The statement read: "Following allegations made to the football club by Doctor Anthonia Onuoha, the club can confirm that a board-led review has been launched into the matter."
Meanwhile, John Hartson last night demanded City sack the person behind the vile e-mail.
The former Arsenal and Wales striker, 36, bravely beat testicular cancer two years ago.
He said: "To take the p*** out of a poor woman fighting cancer just sickens me.
"It's the actions of the lowest of the low. Whoever sent it should be sacked.
"It's shocking and downright despicable.
"They should be punished and punished hard. This is someone at one of the biggest clubs in Europe now.
"I had cancer and came through it. I know what it's like and how it affects people.
"This lady will be going through hell without having to receive an horrendous message like this.
"Anyone who pokes fun at people fighting cancer should take a long hard look at themselves.
"The person is a disgrace."
nah, nothing will happen.. all rats bunch together..
Garry's gone: Cook has his offer of resignation accepted by the Manchester City board of directors following an alleged vile email exchange with the club's football administrator Brian Marwood
Manchester City will begin their search for a new chief executive after they accepted Garry Cook's offer of resignation.
The club launched an internal investigation after claims over an alleged email sent to Nedum Onuoha's cancer-stricken mother.
It was understood that Cook initially claimed his email had been hacked into but has now admitted to an 'error of judgement'.
Cook has also been criticised in the past for a number of public relations gaffes.
In a statement released on the club's official website this afternoon, Cook said: 'I am privileged to have held my position at Manchester City Football Club and to have experienced the opportunities that it has presented.
Centre of attention: Nedum Onuoha's mother Dr Anthonia was copied in to a callous email sent from Garry Cook's account
'The privilege is in part offset however by the significant personal focus which has at times, detracted from the magnificent achievements of those working at the football club.
'It is that factor, together with my error of judgement in this matter that has prompted me to reach this decision, which I believe is in the best interests of the football club.'
The offending email, which was sent 11 months ago, only came to light this week.
In a message intended for City's football administrator Brian Marwood, Cook appeared to mock Onuoha's mother, who was suffering from cancer.
Mistakes: Cook infamously labelled Brazilian ace Kaka a 'bottler' when he rejected a move to City in 2009
Dr Anthonia Onouha was representing her son at the time and was involved in a contract dispute with the club.
In one email to Cook she wrote that while she was 'ravaged with cancer and ongoing chemotherapy" she was still able to fight on her son's behalf.
The reply she received, addressed to 'Brian', read: 'Ravaged with it! I don't now how you sleep at night. You used to be such a nice man when I worked with you at Nike.'
Dr Onuoha this week said: 'When I opened up my emails and saw the message, it was the worst day of my life. Even worse than being diagnosed with cancer.'
Cook apologised on behalf of the club to Dr Onuoha but denied sending the email.
Apology: Manchester City have issued an apology to defender Onuoha's mother
He said an investigation was being undertaken, suggesting the email had been sent by a rogue employee.
However, after further evidence emerged suggesting the email had originated from Cook's iPad, the board looked into the matter.
City's statement read: 'Manchester City Football Club announce that the board-led review initiated on Monday of this week, as a response to allegations made to the football club, football authorities and a national newspaper by Dr Anthonia Onuoha, has been concluded.
'As a result, the club can confirm that there is foundation to Dr Onuoha's allegations and the chairman has written to apologise to Dr Onuoha for any distress caused.
'Following the findings of the review, chief executive officer Garry Cook has offered his resignation, which has been accepted with regret by the board.'