Mitt Romney and Donald Trump embrace after Trump endorsed Romney in the 2012 presidential race. (Julie Jacobson/Associated Press)

Mitt Romney, the 2012 Republican presidential nominee, plans to skip this summer's Republican National Convention in Cleveland where Donald Trump will be officially nominated — an unusual move that underscores the deep unease many Republican leaders have about the brash celebrity mogul as their standard bearer.

A Romney aide told The Washington Post by email Thursday morning, "Governor Romney has no plans to attend convention."

Romney has been one of Trump's chief critics this spring. He delivered a searing, point-by-point indictment of Trump in March — from his business record to his character to his divisive campaign-trail rhetoric.

Trump, who endorsed Romney in 2012 and raised money for his campaign, has since been harshly critical of the campaign that Romney ran. In an interview last month, Trump told The Post that he understood it would be “very hard” for Romney to attend the convention but that he would have no qualms about him being in Cleveland.

“I don’t care,” Trump said. “He can be there if he wants.”

Romney's announcement comes after the GOP's two living former presidents — George H.W. Bush and George W. Bush — announced Wednesday night through their spokesmen that they did not plan to endorse a candidate this year.

Sen. John McCain (R-Ariz.), the party's 2008 presidential nominee, also plans to skip the convention in Cleveland. McCain is facing a potentially difficult reelection campaign in Arizona, a border state with a large Latino population where Trump's hard-line position on immigration may prove polarizing.