Republican Donald Trump skipped the debate where Fox News anchor Megyn Kelly co-moderated. Here's a look back at the clash that started with an earlier debate in August 2015. (Sarah Parnass/The Washington Post)

Former Arkansas governor Mike Huckabee and former senator of Pennsylvania Rick Santorum will attend a pro-veterans rally hosted by fellow GOP presidential candidate Donald Trump on Thursday evening, an event the billionaire real estate mogul organized to counterprogram the seventh GOP debate hosted by Fox News.

Huckabee will attend the event after participating in Thursday night’s "undercard" debate, according to one of his campaign advisers. A Santorum adviser confirmed the former senator's appearance.

Tensions have flared between Fox News and Trump in recent days, beginning with demands from the Trump campaign that the news network revoke reporter Megyn Kelly’s invitation to moderate the debate. Kelly and Trump clashed during the first Republican debate in August after Kelly asked the candidate about disparaging comments he had made about women.

Trump has frequently attacked Kelly’s professionalism since, accusing her of treating him unfairly. At one point, Trump stirred controversy for seemingly referencing Kelly’s menstrual cycle while talking about the tone of her questions. "You could see there was blood coming out of her eyes," he said during an interview on CNN after the August debate. "Blood coming out of her wherever."

The feud escalated after Fox refused to take Kelly off the stage. The organization not only refused to meet Trump's demands, it also released a mocking news release castigating Trump for refusing to participate: “We learned from a secret back channel that the Ayatollah and Putin both intend to treat Donald Trump unfairly when they meet with him if he becomes president.”

Trump’s campaign announced Tuesday that he would not attend the debate, accusing the network of using the billionaire to increase its ratings and advertising revenue. The campaign will instead host an event to benefit a veteran’s charity Thursday night in Des Moines. Doors open at 7 p.m. Central time.

Huckabee told CNN that his participation should not be seen as a slight against Fox News, where he hosted a television program for years.

"I'm not invited to the main stage," Huckabee said. "I would love to have been on that stage."