Mitt Romney Predicts a ‘Bombshell’ In Donald Trump’s Tax Returns

— -- The 2012 Republican presidential nominee, Mitt Romney, has a request for the candidates looking to become the party’s presidential pick this year: release your old tax returns.

And the candidate whose taxes Romney is most interested in reviewing is GOP frontrunner Donald Trump.

“I think we have good reason to believe that there's a bombshell in Donald Trump's taxes,” Romney said in an interview with Fox News’ Neil Cavuto Wednesday. “Either he's not anywhere near as wealthy as he says he is or he hasn't been paying the kind of taxes we would expect him to pay, or perhaps he hasn't been giving money to the vets or to the disabled like he's been telling us he's been doing.”

Romney said he had "no evidence" for his speculation.

“And I'm not saying that's the case. I have no evidence of that. But I'm just saying there are things that could be issues,” he said. "I'm just saying the fact that he is so aggressive in avoiding any discussion of taxes -- of his taxes, and is not willing to put them out so far, suggests that there's something in there he doesn't want us to see."

In an interview on “This Week with George Stephanopoulos” on Sunday, Trump said he would not release his tax records before Super Tuesday.

“We're working on, they're massive,” Trump said, adding later. “At some point we'll release. There's no rush.”

Trump's campaign did not return ABC News' request for comment, but the real estate mogul opened fire on Romney in a tweet.

Trump's personal financial disclosure was released by the Federal Election Commission around the time he announced his run for president last year and Trump tweeted in October of last year a picture showing him signing his tax return.

The Republican candidate wrote four to five checks to national and state veteran groups, including a local veterans shelter in Manchester, New Hampshire, with money that he raised at his Jan. 28 rally in place of the Fox News Republican debate the same night. The Trump campaign also created a website to collect donations, but the names of the organizations aren’t listed.

Following the results of the Iowa caucuses on Feb. 1, where Trump finished second, he held a press conference in New Hampshire and talked about how much he raised in that event. “We raised in one hour, I raised $6 million for the vets, and I would never, ever give that up to go-between first and second in Iowa,” he said. Trump also kicked in $1 million of his own money.

Romney, the former Massachusetts governor, who briefly contemplated a third run for the White House in 2016, called on Trump’s main rivals, Marco Rubio and Ted Cruz, to release the “last few years” of their returns too.

“Frankly the voters have a right to see those tax returns before they decide who our nominee ought to be,” Romney said, noting that he is “so sensitive” to the issue is because he was hammered on it during his own presidential bid four years ago. Romney eventually released his tax returns from 2011 on Sept. 21, 2012.

During a sit-down with reporters on Feb. 16, Rubio said he would release his tax returns "momentarily, any day," but did not give a specific date. ABC News has reached out to Cruz's campaign for comment.

Romney has yet to endorse a candidate in the Republican primary and he did not disclose a timeline for doing so today. Offering his assessment of the current state of the race, Romney said it would be “very difficult” for any one of Trump’s rivals to overtake him “unless perhaps the field narrows.”

“There's no question but that Donald Trump has the clearest path to become the Republican nominee,” Romney told Cavuto.

ABC News' John Santucci, Jessica Hopper and Ines De La Cuetara contributed to this report.