Back in 2007, Wallenberg called Barnevik a "useless business leader who left ABB on the edge of ruin," in a widely seen documentary about the infamous Wallenberg family, produced by public television network SVT.
And now, four years later, Barnevik has dedicated a chapter entitled "The anatomy of a traitor" in his forthcoming book to give his side of the story.
"I was well aware of his weakness in crisis and his vacillation in big decisions. He wasn't someone to take by the hand when it was windy," Barnevik wrote, who feels Wallenberg's claims in the documentary were so outlandish that he wondered if Wallenberg had all of his senses.
"I then got it confirmed from people close to him that he was mentally sane, at least as sane as usual."
After ABB grew out of the merging of Wallenberg's Asea and Swiss Brown Boveri, Barnevik became the company's first head, initiating the long standing cooperation between the two.
But in the beginning of 2000, when Barnevik received the enormous pension of 800 million kronor ($120 million) for his time at ABB, storms blew in Swedish media.
“The board decided my pension,” Barnevik told Dagens Nyheter daily.
“But since (then Investor board chair) Peter Wallenberg went hiding there was nobody there to explain it. Back then he didn't say anything.”
At the same time, ABB had big issues with the asbestos indemnities in the US which almost brought down the industry.
Wallenberg's TV statements a few years later further harmed Barnevik.
Barnevik however points out to Dagens Nyheter that current CEO of ABB, Joe Hogan, couldn't thank him enough for how he built up the company during the 80s and 90s.
He also said the company stock noted all-time-high figues the very same year of the disputed documentary, and he is bitter towards the massive critique.
"Of course Peter Wallenberg's outburst towards me, in front of millions of Swedish viewers, has harmed me in Sweden. For those who have any insight in the matter it has also, no less, harmed himself," Barnevik writes.
"It was bitter since it concerned a person I've worked with fairly close and trustingly, during the more part of 21 years. Therefore it is also with reluctance I'm writing this chapter," he continues.
News agency TT tried to reach Peter Wallenberg for comment, but through an Investor spokesperson siad that he has no comment on Barnevik's book.