Republican front-runner Donald Trump said his "bromance" with 2016 rival Ted Cruz is over on Thursday night following a heated exchange between the two during the sixth GOP debate in North Charleston, S.C., saying the Texas senator was "aggressive" toward him.

"I guess the bromance is over because he hit me, I didn't hit him," Trump told reporters, CNN reported. "I hit him after the fact...There was no reason for him to go that aggressive."

The debate, televised on Fox Business, was filled with fiery exchanges between the candidates, but the most heated moments - those between Trump and Cruz - were most obvious as the two battle for first place in Iowa less than three weeks before the state's caucuses on Feb. 1. Less than a single percentage point separate Trump and Cruz in Iowa, according to RealClear Politics averages, with Trump at 27.3 percent and Cruz at 26.9 percent. In New Hampshire and nationally, however, Trump is well ahead of the rest of the 2016 field.

For most of the campaign season thus far, the two had an unusually friendly relationship for competitors seeking the Republican nomination. That began to change, however, when a secret recording surfaced last month of Cruz questioning Trump's judgment at a Republican fundraiser, The New York Times reported.

The most testy exchanges between the two Republican presidential leaders were over questioning Cruz's eligibility to be president and criticizing the real estate mogul as a symbol of "New York values."

"Back in September, my friend Donald said he had his lawyers look at this in every which way," Cruz said of his eligibility for The White House, CNN reported. "There was nothing to this birther issue."

Cruz attempted to hit Trump as somebody who "embodies New York values," adding that, "Not a lot of conservatives come out of Manhattan" - a poke which allowed Trump to invoke the attacks of Sept. 11, 2001 and the recovery by the city.

"I saw something that no place on Earth could have handled more beautifully, more humanely than New York," Trump said, according to The Atlantic. "The people in New York fought and fought and fought. We saw more death and even the smell of death and it was with us for months."