Former Massachusetts governor and 2012 GOP presidential nominee Mitt Romney on Wednesday called on real estate mogul Donald Trump, the GOP front-runner in the 2016 race, to release his tax returns.

"I think in Donald Trump's case it's likely to be a bombshell," Romney said in an interview with Fox News, speculating the reason the businessman had not made his returns available to the public is because he "may not have as much income" as advertised or, even worse, that he didn't pay any taxes. 

In addition to Trump, Romney also called on presidential hopefuls Sen. Marco Rubio (R-Fla.) and Sen. Ted Cruz (R-Texas) to release their tax returns, although his comments were most pointedly directed at the reality television star who appears to be gliding toward the GOP nomination later this summer.

Romney's decision to speculate openly about the details of Trump's taxes is ironically similar to that of then-Senate Majority Leader Harry Reid (D), who infamously claimed in 2012 that Romney "didn't pay any taxes for 10 years." The tactic incensed the Romney campaign, which charged that Reid was floating nonsense without a shred of evidence.

An aide to Reid said the senator was tickled when he heard Romney's words, marveling that of all people, it was the 2012 nominee making these insinuations.

"Couldn't they get someone else to do it," he said, laughing.

Romney released his 2010 tax returns and 2011 estimates in January of 2012, following the lead of former House Speaker Newt Gingrich, then his main GOP rival in the 2012 presidential race. But he did not release more years of returns until September, showing he paid an effective tax rate of less than 15 percent.

Trump said in a Monday interview that he would "get them out at some point, probably." 

“I mean, I’m looking at it. I told my people the other day, start looking at it," Trump told conservative radio host Hugh Hewitt.

At a rally in January, Trump bragged that he paid "as little as possible" in taxes because that's "the American way."

Trump didn't take too well to Romney's suggestion on Wednesday.

Mitt Romney,who totally blew an election that should have been won and whose tax returns made him look like a fool, is now playing tough guy

— Donald J. Trump (@realDonaldTrump) February 24, 2016