Former New York City mayor Rudy Giuliani has apologized after being caught brazenly lying about Hillary Clinton's response to the September 11 terrorist attacks.

The ex-mayor said he 'made a mistake, I'm wrong, and I apologize' after claiming earlier in the day Clinton did not visit Ground Zero in the immediate wake of the attack.

Giuliani made his incorrect comments while speaking to Donald Trump supporters at a rally in Ocala, Florida, on Wednesday.

'Don’t tell me if you said that you remember Sept. 11, 2001. I remember Sept. 11, 2001. Yes, yes, you helped to get benefits for the people who were injured that day,' the former mayor said in reference to the work Clinton did as Senator for New York to support victims of the attack.

Former New York City mayor Rudy Giuliani has been caught brazenly lying about Hillary Clinton's response to the September 11 terrorist attacks

'But I heard her say that she was there that day. I was there that day, I don’t remember seeing Hillary Clinton there,' Giuliani (pictured standing next to Hillary Clinton) said

'But I heard her say that she was there that day. I was there that day, I don’t remember seeing Hillary Clinton there.

'I lost so many friends on Sept. 11, I think about it every day. Don’t tell me you belong to our very, very tight group of ‘never forget.’ Don’t tell me that,' he told Raw Story.

But Giuliani's claims have been undone by photographs taken on September 12 that show Clinton not only in Manhattan, but walking side-by-side with the former mayor.

The political duo was pictured with then-New York governor George Pataki.

Giuliani's claims about Hillary have been undone by a series of photographs taken on September 12 that show Clinton not only in Manhattan, but with the former mayor

Rudy Giuliani and Hillary Clinton are seen together at St Patrick's Catherdral in New York in 2000

Clinton has often described being in Washington - where congress was in session - when hijacked jets began striking the World Trade Center and the Pentagon, before travelling to New York on a federal plane on September 12.

While there, she toured the devastated area on foot, and also circled the smoldering rubble in a helicopter.

Last month, the Democratic nominee described what she saw as: 'as close to a depiction of hell that I've ever personally seen'.

Donald Trump greets former New York City Mayor Rudolph Giuliani at a campaign rally in Wilkes-Barre, Pennsylvania, October 10

Rudy Giuliani has previously praised the work Hillary Clinton did in the aftermath of the September 11 attacks

'There weren't that many survivors; the ones that did survive were grievously injured. The loss of life was overwhelming," she told CNN last month.

'But it was also my job and the job of other officials to get our city and state and country what we needed.

'I would meet these shattered lives of people where they were broken, but I saw so many of them strengthen and show such resilience. So I felt privileged.'

Hillary Clinton greets Rudy Giuliani in 2008, when they were presidential candidate hopefuls for their respective parties

Giuliani's comments contradict some he made earlier this year, when he praised Clinton for her work in the wake of the attack.

'Hillary Clinton, like Senator Schumer, like the entire Senate and House of Representatives, like every Republican and Democrat that I know, was enormously helpful,' he told the Washington Post in July.