Alex Ferguson and Roy Keane have gone to war after the former Manchester United manager savaged his former Irish “Captain Fantastic” in his new book.

Fergie’s latest autobiography, set to hit the shelves on Thursday, features several controversial comments with regard to the Cork hero.

Ferguson says Keane was wrong in Saipan during the 2002 World Cup bust-up with Irish boss Mick McCarthy, undermined Ferguson’s authority as boss in his final days at Old Trafford and failed spectacularly despite spending a fortune as a manager when he retired.

Offered the chance to reply when he appeared on ITV’s Champions League show on Tuesday night, Keane hit back and claimed Ferguson doesn’t know the meaning of the word loyalty.

Keane blasted, “I’m okay, quite relaxed. I remember having conversations about loyalty when I was at the club and I don’t think he knows the meaning of the word.

“To constantly criticize other players that brought him success ... I won’t be losing any sleep over it.

“I just don’t think the manager needs to do it. I don’t know how many books he’s written now. A lot of these players helped win a lot of trophies. It’s just part of modern life. People like to do books and criticize ex-players.”

Ferguson argues in the book that he had no choice but to release Keane in 2005 and pay up his contract before he signed for Celtic.

Ferguson revealed on Tuesday that Keane had “slaughtered” several of his teammates in an interview for United’s in-house channel MUTV in 2005.

“Given the nature of the man you can expect a response. That is the type of personality Roy is,” Ferguson said in a press conference to publicize his book, "My Autobiography."

Ferguson also writes in the book of Keane’s fiery temperament. “What I noticed about him that day as I was arguing with him was that his eyes started to narrow, almost to wee black beads. It was frightening to watch. And I’m from Glasgow,” Ferguson wrote.

Despite criticizing Keane in his book, Ferguson will never forget the midfielder’s efforts on the pitch for United, with whom he won seven league titles.

“We did well by him,” Ferguson added in his press conference.