Colby Covington's vile remark about Leon Edwards' late father threatened to cause chaos at the UFC 296 press conference.
Brit Edwards sat alongside his American rival Covington in Las Vegas to speak ahead of the fight, but things turned personal midway through the open event inside MGM Arena.
'I'm bringing you to the seventh layer of hell,' Trump-supporting Covington told Edwards, before adding: 'We'll say "what's up" to your dad while we're there.'
Edwards' demeanor quickly changed and he threw a bottle at his rival, who was wearing a 'Make America Great Again' cap, as well as fancy dress as George Washington.
The bottle struck Covington, leading to both fighters immediately standing up to confront each other before security stepped in to separate them.
Colby Covington came to the UFC 296 press conference in fancy dress on Thursday afternoon
Tempers frayed between the pair when Covington made a joke about Leon Edwards' dad
British fighter Edwards was calm until Covington made a distasteful joke about his late father
Covington's jibes at the press conference were largely light-hearted, if occasionally distasteful, until he overstepped the mark by a considerable distance.
Edwards immediately leapt to his feet and tried to get at Covington, with security swiftly intervening.
Covington then continued: 'Little f*****g p***y. Ultimate Feeling champion he isn't an Ultimate Fighting champion. Better get the tissues ready.'
The crowd then started chanting 'USA', before Covington said: '1776 baby. This is the American revolution. General Washington started it, General Covington ends it.'
Edwards' father was shot and killed in a London nightclub when the MMA star was just 13. 'Rocky' has since said he believes the motive of the murderer was a dispute over money.
Edwards was raised by his mother and has previously recalled being told the tragic news about his father when he was a young teen.
Edwards, pictured here (L-R) with his sister, mother and grandmother - credits his mum as the most important influence on his life
Edwards and Covington faced off ahead of their huge main event at UFC 296
He said: 'It was probably like 2am. I was in my room. Mum was in her room. We hear the phone ringing. I heard her crying, and I knew from then something bad, you know.
'Eventually, she came into my room and just told me this, your dad’s just got killed in London. It was something to do with money. I don't know what exactly. It was some mad s***, but I knew that it could happen.
'It f****d me up. It pushed me more into gang life and crime, toward the negative. My mid-teens were my darkest years,' he said.
Edwards is usually incredibly cool but evidently Covington's grim jibe was beyond the pale and provoked the reaction he no doubt sought.
'Keep that same energy backstage', he told the challenger to his welterweight title.