|Warning: Some of the language in this story may cause offence.|
Floyd Mayweather directed a homophobic slur at Conor McGregor after accusing him of making racist comments during the media tour to promote their Las Vegas fight.
Former five-weight boxing world champion Mayweather will face UFC lightweight title-holder McGregor in 12 rounds under boxing rules in August.
"He called black people 'monkeys'," said the American, 40, during a news conference at Wembley Arena on Friday.
Then, once the pair entered a boxing ring at the event for the official promotion, Mayweather addressed McGregor as: "You punk. You faggot. You ho."
The two men have conducted a series of news conferences in recent days to promote the fight, with stops in Los Angeles and Toronto before the trips to New York and London.
The 29-year-old Irishman has attracted criticism for a series of comments during those events and is alleged to have made racist comments during the third stop of the tour in New York on Thursday.
"He totally disrespected black women," added Mayweather. "Then he spoke disrespectfully to my mother and he spoke disrespectfully to my daughter."
The American added on Friday: "Racism still exists. I'm not going to stoop that low and speak about his like or speak about his child. I'm glad that he just had a healthy child and he has a beautiful family."
Responding to Mayweather at the New York press conference on Thursday, McGregor said: "I'm a multicultural individual and I don't have any ill feelings towards anyone. I don't even see colour."
Then, speaking to BBC Sport after the London event, he said: "I know who I am, people around me know who I am. We know his history, but I didn't bring it up. The fight game is ruthless and it's what I expect."
In 2010, Mayweather made racist and homophobic remarks towards Filipino boxer Manny Pacquiao in a video posted on the website Ustream.
'It's about taking risks'
At the end of the news conference, Mayweather and McGregor took several questions from the media.
BBC boxing correspondent Mike Costello asked McGregor - who has never boxed as an amateur or professional - how he addresses pundits who say he has no chance of beating Mayweather.
McGregor replied: "I do what I say I'm going to do, by sleeping [Mayweather] inside of four rounds - the same way I silence them every time."
Mayweather, who won all 49 of his bouts, was asked how he thought the McGregor fight would affect his legacy in boxing.
"In boxing, it's all about taking chances," he said. "In contact sports, it's about taking risks, so if you going to take a risk, take it against the top guys."
BBC Radio 5 live sports news correspondent Richard Conway
The four-night global promotional tour is over and will reassemble in Las Vegas in the build-up to the contest on 26 August.
Thousands of fans packed Wembley Arena cheering and shouting McGregor's name. Chants of "pay your taxes" and "sit down, shut up" were continually chanted at Mayweather.
This was more pantomime than press conference. But troubling elements of this fight have emerged before the question of its sporting validity is even answered.
Sexist and homophobic language was used continually. The hype and hoopla - what should have been a carnival of over the top bravado - sadly had a misogynistic and backdated overtone.