Cooper Allen

USA TODAY

Mitt Romney may not be a candidate in the 2016 GOP presidential race, but that doesn't mean he can't affect the debate.

Romney this week suggested that there could be a "bombshell" in Donald Trump's tax returns, prompting a furious counter from Trump. At Thursday night's debate in Houston, Trump explained that he's currently under "a very routine audit" and that once it's complete, he'd release the returns.

"Because of the size of my company, which is very, very large, I'm being audited," Trump explained, saying it's occurred continually over the years.

Texas Sen. Ted Cruz, like Romney, suggested there was more to it than that.

"He's afraid," Cruz said, of what the fallout could be.

Romney weighed in on Twitter shortly after the exchange: