The worst investment shareholder activist Daniel Loeb ever made was the result of a bad tip from a former friend, fellow activist Bill Ackman. In fact, the investment was so bad that Loeb apparently still can’t forgive Ackman for getting him involved, the FOX Business Network has learned.

That was the upshot from a private briefing Loeb gave to a group of analysts and investors in New York on February 25. When asked during the talk about his biggest flub as an investor, a visibly agitated Loeb said  he lost nearly his entire investment in an Ackman fund that invested in shares of Target (TGT), according to one person who was present.

Like most of Ackman’s “activist” investments, the fund was designed to prod Target to make management and other changes to boost its share price. But this person said that as Loeb explained it during his presentation, before finally pulling out of the fund, he barely recovered “10 cents on the dollar” by taking Ackman’s advice.

“He (Loeb) made it clear he wasn’t a big fan of Ackman and that the takeaway from the experience is don’t invest your own money based on someone else’s investment idea,” this person said.

Ackman launched the Target fund in 2007, and enticed other hedge fund managers like Loeb  to put in money. But during the financial crisis of 2007 and 2008, the fund suffered heavy losses which were exaggerated by Ackman’s use of options. Loeb is said to have pulled money out of the fund in February 2009, but his timing was just as bad, he explained. Returns bounced back a bit just after he yanked his money out.

Still, Loeb said he had no regrets cutting his losses. “So I would have recovered 20 cents on the dollar -- big deal,” he explained to the crowd of about 70 people, the person who attended said.

When asked for a response about the event, a spokeswoman for Loeb’s Third Point hedge fund said in an email  “We generally don’t comment on private, off-the-record meetings. Sorry!” A spokeswoman for Ackman’s Pershing Square hedge fund didn’t return a call for comment; Ackman didn’t return an email request for a comment.

Loeb and Ackman -- who are both considered activist investors -- have a famously icy relationship and people who know both men trace their hard feelings to Loeb’s ill-fated Target investment. In early 2013, Loeb profited by buying shares of nutritional supplement seller Herbalife, after Ackman shorted the stock calling the company an illegal pyramid scheme and stating that shares would fall to zero.

Shares of Herbalife rebounded after investments by Loeb and financier Carl Icahn, who is also an Ackman critic. Loeb cashed out of his Herbalife position a few months later, at one point chiding Ackman in an email saying, "Never interfere with an enemy when he is in the process of destroying himself."

Shares of Herbalife have been floundering of late after, as first reported by FOX Business, the Federal Trade Commission launched a civil antitrust probe into Ackman’s charges that the company is a pyramid scheme because it earns most of its money selling distributorships, rather than products such as protein shakes.

During the February meeting, Loeb also criticized New York mayor Bill de Blasio over his opposition to charter schools in New York City, which operate in low-income neighborhoods and are financed by private donations.

Loeb is a proponent of charter schools, but his jabs at de Blasio were said to be less caustic than those aimed at Ackman. “What he said about de Blasio was much softer than what he was saying about Ackman,” the attendee said.

Charles Gasparino joined FOX Business Network (FBN) in February 2010 as Senior Correspondent.