Amid speculation over whether Donald Trump Jr. may be mulling a run for New York City mayor, failed candidate Anthony Weiner offered an opinion that sparked a snarky response from the younger Trump.

Asked by a TV news reporter Tuesday about the possibility of a Trump Jr. run for mayor, Weiner said, "I'd come out of retirement just to beat him like a rented mule."

Trump Jr. tweeted in response: "Too soon Anthony!!! You probably shouldn't be talking about beating anything ever again. Go back to your cave."

The scandal-scarred Weiner badly lost the Democratic primary of the New York City's mayoral race in 2013. By that time, he'd been caught in two sexting scandals, once in 2011, when he used Twitter to send provocative photos of himself while in Congress, and again in April of 2013, shortly after he announced he was entering the mayoral race. That's when revelations of an online relationship with a woman named Sydney Leathers surfaced.

Weiner, 51, appeared on "The Late Show With Stephen Colbert" Monday night after The Democratic National Convention in Philadelphia, where his wife Huma Abedin -- longtime top aide to Hillary Clinton -- was working.

He told Politico in 2014 his political career was "probably over" and that he planned to stay busy with business, media appearances and his son with Abedin, Jordan.

Trump Jr., 38, meanwhile, has refused to rule out a run for mayor after his appearance at the Republican National Convention last week. He said on CNN's "State of the Union" show: "As my father has always said, I want to -- we always like to keep our options open."

Mayor de Blasio said he welcomes the challenge.

"In terms of Donald Trump Jr., I will predict something right here and now," he told Politico. "That his father and his values will be rejected soundly by the people of New York City in November. So, if after that he thinks that it’s a great idea to run against me, be my guest."