Former New York mayor Rudolph W. Giuliani endorsed his one-time political foe Mitt Romney for president Monday, saying that the former Massachusetts governor has won the Republican nomination “fair and square.”

Former New York City Mayor Rudolph W. Giuliani speaks at the National Press Club in Washington in this Sept. 6, 2011, file photo. (SAUL LOEB/AFP/GETTY IMAGES)

Putting aside years of animosity with Romney following the 2008 presidential race, Giuliani said he met Romney for breakfast last week and, after pressing him on economic and foreign policy matters, concluded he would be the GOP’s best standard bearer.

“I think that Mitt has won fair and square,” Giuliani said during an interview Monday morning on Fox News. “He’s proven he’s the most effective Republican, he’s taken on everybody and won an incredible number of primaries, and he’s got the resume and background for the job.... Who better than Mitt Romney to carry our banner?”

A hint of the endorsement came earlier this month when Guy Molinari, Romney’s New York chairman and a Giuliani confidant, predicted that the former mayor would back Romney despite their “bad blood.”

Giuliani said he would have been inclined to support former House speaker Newt Gingrich, a longtime friend, had he waged a more effective campaign. He said he settled on Romney over the past week.

Giuliani said “there’s no doubt about it” that his stinging 2008 rivalry with Romney left lasting animosity between the two. But now, Giuliani said, he is willing to do “anything I could” to help Romney defeat President Obama.

“I don’t think the Democrats have any idea what they’re running against,” Giuliani said on Fox. “Mitt Romney’s a tough, tough campaigner, and his campaign organization is really tough.”

In a statement his campaign released following Giuliani’s endorsement, Romney said: “I’m very proud to earn the support of such a distinguished leader and public servant to our country. Rudy’s successes in turning around New York City are well-known and his name is synonymous with leadership, uniting a city in the aftermath of the worst terrorist attack in our nation’s history. I look forward to his help in the months ahead as I work to restore America’s promise and reverse President Obama’s failed policies.”