Meanwhile the elder Trump denies his son will run for New York mayor

Trump Jr responded on Twitter, telling him: 'Go back to your cave'

Said only thing that could make him go back to politics is if a Trump ran

Anthony Weiner is currently in Philadelphia for the Democratic convention

Anthony Weiner has sworn he would come back into politics if Donald Trump Jr ever ran for New York mayor - a pledge met with an acerbic tweet on Trump Jr's part.

The former congressman is currently in Philadelphia for the Democratic National Convention. He flew there hours after calling the elder Trump a 'xenophobic, narcissistic, racist anti-Semite' on Stephen Colbert's Late Show.

Weiner ended his political career after losing his seat at the US House Of Representative and the 2013 New York mayoral election to two sexting scandals.

But the former congressman, whose wife Huma Abedin is one of Hillary Clinton's closest advisers, pledged on Tuesday on Fox 5 that he could make a political comeback if Trump Jr decided to run for New York mayor.

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Anthony Weiner (pictured on Tuesday at the Democratic National Convention in Philadelphia) has vowed to come back into politics to defeat Donald Trump Jr, should he ever run for New York mayor

Weiner wouldn't even want to actually stay as the mayor, he said, but would run for the sole purpose of defeating Trump Jr.

'The only thing that could make me come out of retirement and run for mayor again is if anyone named Trump ran,' Weiner told Fox 5.

'I would come out of retirement just to beat him like a rented mule and then I'd turn the keys back over to de Blasio.'

Trump Jr replied on Twitter, writing: 'Too soon Anthony!!! You probably shouldn't be talking about beating anything ever again. Go back to your cave.'

Meanwhile the elder Trump told Fox 5 in a statement that his eldest son has 'no intention of running for mayor of New York'.

Trump Jr (pictured at the Republican National Convention in Cleveland last week) said in a CNN interview that he would 'love' to run for mayor - but his father said in a statement that his eldest son had no intention to do it

Weiner's pledge to come out of retirement to defeat Trump Jr in a potential mayoral election was met by an acerbic tweet on Trump Jr's part (pictured)

Trump Jr made a slightly different claim on CNN's State Of The Union last week. He started by telling host Jack Tapper that his main priority until November will be his father's campaign.

But when Tapper asked whether Trump Jr would consider running for office himself after that deadline, Trump Jr replied: ' Well, I never like to rule anything out, Jake. You know, I want to keep optionality.

'As my father has always said, I want to - we always like to keep our options open. So if I can do that as a service to our country I’d love to do it.'

New York City will elect its next mayor in November 2017 - one full year after the 2016 presidential election.

Bill de Blasio, the current mayor, will be eligible to run for a second term. He won the November 2013 election - the same one that saw Weiner's downfall.

Weiner resigned from Congress in 2011 after posting an explicit photo of himself on his Twitter account and admitting he had had similar exchanges with several women over the past years.

He tried to make a comeback in 2013 by running for mayor and established himself as a strong contender until more photos surfaced, revealing that Weiner had continued sending explicit images after his resignation.