Toronto mayoral candidate Adam Giambrone has now admitted to "multiple" affairs with women other than his partner. (CBC)

Adam Giambrone has dropped out of the Toronto mayor's race after publicly admitting to having had a number of intimate relationships with women other than his live-in partner.

Once hailed as the boy wonder of Toronto politics, Giambrone's week-old mayoral campaign is finished, and his political future in doubt.

Giambrone didn't make the announcement about the mayor's race himself — even though he held a news conference at Toronto City Hall on Wednesday morning to apologize for having sexual relationships with women other than his live-in partner.

Instead, several minutes after Giambrone left the stage, his executive assistant walked before the cameras, re-read Giambrone's statement and then added his boss's run for mayor ends "as of today."

Before leaving the podium, Giambrone made a number of abject apologies to his family, friends and supporters.

Reporters were caught by surprise when he left the news conference refusing to answer questions. A few minutes later, his assistant Kevin Beaulieu read the statement again, apparently adding what Giambrone couldn't bring himself to say — that he is dropping out of the race.

It has been two days of surprise developments in Toronto politics.

On Tuesday, Giambrone appeared on the front page of the Toronto Star with the newspaper reporting he had had an affair with a Toronto university student, while claiming a partnership with Sarah McQuarrie.

McQuarrie was introduced amid the pomp and glitz of Giambrone's campaign launch last week as his long-time partner. Friends say Giambrone and McQuarrie have been together for about five years.

On Wednesday, Giambrone was back on the front page of the Star, admitting he hadn't been completely forthcoming in the first report.

Calling it the "worst mistake of my life" Giambrone admitted to having an intimate relationship with a woman who was not his partner — and then subsequently admitted to affairs "with other women."

On Wednesday, the Star published a transcript of another apology from Giambrone which showed he had been less than frank when first asked about his relationship with student Kristen Lucas.

"I have no excuse for my failure to disclose my relationships with other women," Giambrone said in his statement. He did not offer any further details about the women's identities or how many women he was referring to.

"In an effort to bring this chapter to a close, let me say I did have intimate relationships for a period that lasted throughout most of last year with women other than my partner. I apologize to them for the hurt I have caused. I regret deeply not having made this full disclosure earlier to Sarah [McQuarrie], my partner, and to my family my friends and my supporters as well."

The 32-year-old city councillor and chair of the Toronto Transit Commission was first accused by 20-year-old Kristen Lucas of having an affair which included having sex on the couch in his office at City Hall.

Lucas also said Giambrone told her in advance of the decision to raise TTC fares last year.

The university student said Giambrone told her McQuarrie was by his side for "political" reasons only.

Lucas said the two had been having a relationship for more than a year and "on several occasions, [they] had sex late at night on a couch in [Giambrone's] City Hall office."

Giambrone's statement says he will continue on as city councillor and as chairman of the much criticized Toronto Transit Commission.