By Tom LoBianco and Jim Acosta CNN

WASHINGTON (CNN) -- Mitt Romney won't attend the Republican National Convention this summer, joining four previous nominees in skipping the event and underscoring the deep divide inside the GOP over Donald Trump becoming the party's standard-bearer.

An aide to Romney said Thursday that the former Massachusetts governor would not go, despite accepting the nomination at the convention four years ago.

With Trump as the party's presumptive nominee, whether to attend the convention has become the latest front in an internal party struggle over how to handle the billionaire businessman's role in the GOP.

A spokesman for former President George W. Bush said yesterday that he would not be attending and a spokesman for his former President George H.W. Bush said he would not attend either. Jeb Bush, who ran for the Republican presidential nomination, told CNN earlier this year that he would not attend the convention.

Sen. John McCain, the 2008 Republican nominee, announced last month he was skipping the convention. The only other living former Republican nominee, Bob Dole, will attend he convention, his spokeswoman told CNN.

House Speaker Paul Ryan, who also serves as chairman of the Republican National Convention, encouraged fellow members of his party to attend.

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