"I don't know what happened to him," Trump said during a rally in Portland, Maine. "You can see how loyal he is. He was begging for my endorsement. I could have said, 'Mitt, drop to your knees.' He would have dropped to his knees."
Just hours before Trump, Romney gave a speech blasting the reality TV star
as bad on foreign policy and lacking the temperament to be president.
"Think of Donald Trump's personal qualities, the bullying, the greed, the showing off, the misogyny, the absurd third grade theatrics," he said. "We have long referred to him as 'The Donald.' He is the only person in America to whom we have added an article before his name. It wasn't because he had attributes we admired."
But Garrett Jackson, a former personal aide to Romney, later tweeted on Thursday that the former Massachusetts governor never "begged" Trump for his endorsement -- adding that he wished "I would've recorded Trump kissing Mitt's ass."
Trump went on an extended rant about Romney, while also making time to jab at Democratic front-runner Hillary Clinton and Florida Sen. Marco Rubio, whom the brash billionaire will face off against during a debate Thursday night.
"Mitt is indeed a choke artist," Trump said. "He choked like I've never seen anyone choke. Other than Rubio."
Trump blasted his two remaining obstacles to the Republican nomination, Rubio and Ted Cruz, painting them as bought by special interests.
"I tell people if you had a lightweight like Rubio as president, he's all controlled by the special interests, 100%. He gets all his money. Remember, I'm self-funding, they're not paying me anything," Trump said. "If you have a guy like Ted Cruz getting a lot of money, a lot, from oil and other places. So I mean, honestly, that's the way life works. So what happens is oil, 100%. They'll get a lobbyist, they're took care (of), they're not going to do anything. Me, it's different."
However, a source with knowledge of the Trump campaign's plans said Trump is planning to start a fundraising blitz after clinching the Republican nomination.
Trump also said that his net worth is more than Romney's, claiming that one of his New York properties alone is worth more than the former Massachusetts' governor's net worth.
The real estate mogul also continued to reject Romney's claim that Trump could have a "bombshell" in his tax returns, which he has not released, citing an ongoing audit.
Trump did not have all bad things to say about the Romneys, however, praising Mitt's wife Ann as "a lovely woman."