Sir Alex Ferguson wrote in his autobiography that Roy Keane had "the most savage tongue you can imagine" and it would appear clear where he got it from – his mother!
Mrs Keane is the latest person to weigh in on the explosive revelations from the book, saying she is unhappy with comments made by the Manchester United legend about her son.
"God Almighty, I can’t believe Sir Alex would say such things about Roy," Marie Keane told the Irish Sun.
"I just can’t believe it. I would never have thought he would do something like this.
"He’s our son and he has a wife and children and it’s not nice for any of us to be hearing someone run a loved one down like that … It’s all very nasty what he said. It’s nasty really. It’s terrible and I’m very upset."
Keane himself also accused Ferguson of disloyalty towards his former players after details of the Scot's controversial autobiography emerged on Tuesday.
In 'My Autobiography', there is criticism of former United men Ruud van Nistelrooy and David Beckham among others, but Keane is the biggest casualty, mainly for a tirade against his team-mates on the club's in-house channel MUTV which was never broadcast.
In the interview, which followed United's defeat to Middlesbrough, Keane described Kieran Richardson as a "lazy defender" and said he doubted why "people in Scotland rave about Darren Fletcher". Keane also criticised Edwin van der Sar and Alan Smith.
He also railed at Rio Ferdinand, saying "just because you are paid £120k a week and play well for 20 minutes against Tottenham, you think you are a superstar".
Keane says he "will not lose sleep" over the revelations, but the former Sunderland manager is upset by the way the Scot has spoken openly about other United players who brought him so much success during his 27-year reign at Old Trafford.
"I do remember having conversations with the manager when I was at the club about loyalty and, in my opinion, I don't think he knows the meaning of the word," Keane told ITV1.
"It doesn't bother me too much what he has to say about me but to constantly criticise other players at the club who brought him a lot of success, I find very strange.
"But I won't be losing any sleep over it."
He added: "I just don't think the manager needs to do it. I don't know how many books he's written now but he has to draw the line eventually to say 'listen these players have all been top servants to Man United'.
"And a lot of these players helped the manager win lots of trophies so imagine if we'd never won a trophy what he would have said.
"We brought success to the club, we gave it everything we had when we were there.
"But, as I said, it's just part of modern life now, people like to do books and criticise their ex-players."
Ferguson lifted the lid on his feud with Keane in the book, claiming he had no option but to offload the increasingly volatile player in 2005.
The final straw came when Keane accused Ferguson of bringing his own dispute with shareholder John Magnier over the Rock of Gibraltar racehorse in to the club.
"Given the nature of the man you can expect a response. That is the type of personality Roy is," the former United boss told a press conference.
"We had to react to the situation so quickly because his actions were so quick. For one reason or another he decides to go and criticise his team-mates.
"Most of you won't have seen the video but you couldn't release it. You just couldn't.
"It ended up with two of our young players being booed before a Champions League match in Paris because of it.
"We decided we had to do something. The meeting in the room was horrendous. I just couldn't lose my control in this situation.
"If I had let it pass and allowed it to happen the players would have viewed me differently. Much more differently to how I would have liked to have been judged.
"Throughout my career I have been strong enough to deal with important issues like that. Roy overstepped his mark. There was no other thing we could do."