Trump during the primary campaign resorted to unusually extreme rhetoric - including a distasteful reference to menstruation - in his attacks on Kelly, one of the most powerful women in American television and the star of her own cable news show.
After being branded a misogynist and xenophobe during the bruising primary campaign, the apparent Republican nominee has been softening his image, and in a recorded interview broadcast late Tuesday publicly buried the hatchet with Kelly.
"When I'm wounded, I fight back hard," Trump explained when pressed by Kelly about the reason for his bare knuckles, no-holds-barred style, describing himself as a "counterpuncher" on the campaign trail.
Kelly, a former corporate litigator, joined Fox News in 2004 as a television reporter from Washington DC, rising rapidly through the ranks thanks to her good looks, fierce ambition and keen intellect.
In 2014 she was the only female journalist listed on Time magazine's list of the world's 100 most influential people.
Her run-in with Trump last August during the first Republican TV debate of the 2016 election catapulted her to even wider fame.
She and two male colleagues moderated the debate, which attracted a record 24 million viewers. Trump took offense to her tough questions, insinuating that she treated him unfairly because she was menstruating.
"You could see there was blood coming out of her eyes, blood coming out of her - wherever," he told CNN after the debate.
In hindsight Trump conceded Tuesday that he might have been a little rough in his handling of Kelly and others at whom he has directed his attacks during the campaign.
"I could have done certain things differently. I could have maybe used different language in a couple of instances," Trump said.
But, having vanquished all 16 other Republican contenders and having brought an initially reluctant party establishment largely on side, "I have to be very happy with the outcome," he added.
As recently as March Fox News called out the brash billionaire for having a "sick obsession" with their glamorous marquee star.
"Donald Trump's vitriolic attacks against Megyn Kelly and his extreme, sick obsession with her is beneath the dignity of a presidential candidate who wants to occupy the highest office in the land," Fox News said in a statement, accusing Trump of an "endless barrage of crude and sexist verbal assaults" against her.
The 45-year-old blonde mother of three - who was attacked not only by Trump, but also online by legions of his followers - took the initiative in trying to reach a truce.
She requested a meeting with the billionaire real estate mogul one-on-one last month at his Trump Towers offices, ahead of Tuesday's prime-time interview.