Billionaire investor Carl Icahn sauntered onstage on 13 September 2016 to face a standing room-only crowd in New York City’s luxurious Pierre Hotel ballroom. The Wall Street crowd, attendees at the annual CNBC Institutional Investor Delivering Alpha conference, had waited until 5 p.m. to hear one of the giants speak. The Dow had fallen almost 200 points that day, as market seers from Ray Dalio to Paul Singer warned of doom, spooking investors inside and outside the room. Icahn, too, is pessimistic on the stock market, taking a massive short position that has been pushing his investment fund deeper into the red for more than year. What would he say?

Icahn, however, wanted to talk about a stock he professes to be bullish about: Herbalife, the nutritional supplements company that recently reached a $200 million settlement with the Federal Trade Commission over what the agency alleged were fraudulent practices. Icahn now has a 21% stake in the company, and five of his men serve on its board. That’s only part of the story, of course. When it comes to Herbalife—at least, in the mind of investors—Icahn’s financial ambitions are wrapped inside his high-profile feud with hedge-fund manager Bill Ackman, who has made a massive bet that Herbalife shares will collapse.

There’ve been plenty of rounds in the Icahn vs. Ackman steel-cage bout and the most recent occurred last month, when the Wall Street Journal reported that Icahn had asked Jefferies, his longtime banker, to shop his shares, and Ackman promptly appeared on CNBC to gloat about it.

“I am telling you that I’m not just playing games buying the stock,” Icahn said at the Delivering Alpha conference. He then upped the ante. “I’ve gone to the FTC to get accelerated treatment for the right to go to 50%” in Herbalife, he said. Indeed, Icahn intimated he might go further even than that. Prompted by CNBC’s Scott Wapner, who was interviewing him, the investor said he would “consider” a tender offer to buy the whole company. Icahn quickly admitted, “I don’t have any stated intention to do it….it’s something I’ve thought about. Doesn’t mean I will. And I think there are other people that might. I think Herbalife is certainly a candidate to go private.”

Few activist investors signal their intent to increase their stake in a particular company or buy it outright. After all, such news would only make their target more expensive. But a tender offer, Icahn said at the Pierre, would create a massive short squeeze in Herbalife. And the biggest short in Herbalife, of course, is Ackman.

“Ackman loves to think I’m going away,” Icahn said. He spent half of the interview bolstering the notion he was sticking around. But Ackman’s views, at least on Icahn’s attempt to bail out of Herbalife, weren’t mere speculation.

Bill Ackman Gets a Text

On Thursday evening, Aug. 4, as Ackman was vacationing in Venice, the hedge fund billionaire received an unexpected text. It was just after midnight in Italy and the sender asked if Ackman could meet him in New York City the next day.

The text was from a senior Jefferies executive. Ackman didn’t know the man well, and hadn’t done business with Jefferies in the past. But he did know someone who had: Carl Icahn. Ackman was planning to return to New York the next day on his Gulfstream and spend the weekend at his Bridgehampton home. He asked, “Can it wait until next week?” The banker didn’t think so, insisting on a phone call instead.

It is now known that Jefferies was looking for a buyer for Icahn’s stake this summer, and that Icahn may have been open to selling. Also known is that Ackman was contacted, and considered buying part of Icahn’s stake. But most of the details of how the events unfolded have never been reported. This is a portrait of a series of spy-vs.-spy investing machinations—infused with a potent dose of ego, contempt, and rivalry—that provides a fascinating window into how two billionaire investors operate. (Icahn did not return calls seeking comment from Fortune, but he has publicly asserted that he never gave Jefferies an order to sell his shares.)

In the end, despite at least a month of scouring Wall Street, and hamstrung by legal restrictions (more on that later), the best bid Jefferies was able to get Icahn was for a little more than 11 million, of Icahn’s 17 million, Herbalife (HLF) shares at a price of $51.50 a share—about $10 south of where shares of Herbalife were trading on the open market at the time, sources familiar with the bid said. (People close to Jefferies put the figure a few dollars higher.) It didn’t take Icahn long to reject the bid.

On Tuesday at the Delivering Alpha Conference, when asked whether he had been considering selling his stake, Icahn smiled and asked for the next question.

The Long Running Feud

The mutual antipathy between Icahn and Ackman is the stuff of Wall Street legend, a longstanding on-again, off-again conflict between two pugnacious billionaires, the 80-year old lion and his silver-haired 50-year-old antagonist. It began back in 2003, when Ackman sold Icahn his hedge fund’s stake in a publicly traded real estate company, with the agreement that Ackman’s investors would get a slice of the upside. But after Icahn flipped the company for a 75% profit, he declined to share the gains. Ackman sued, and animosity has followed ever since. (Ackman was awarded a judgment that ultimately came to $9 million with interest.)