Delivering Alpha

Guess who bro hugged? Yep. Ackman, Icahn

When rivals team up: The Wall Street edition
When rivals team up: The Wall Street edition

The feud between Bill Ackman and Carl Icahn appears to officially be over.

The billionaire activist investors—who famously brawled over the phone live on CNBC in January 2013—shared the stage during a surprise joint appearance Wednesday at the Delivering Alpha conference presented by CNBC and Institutional Investor.

"You have to respect that record," Ackman said of Icahn's investment history.

"Where we share a lot of commonality is the importance of shareholders to have a voice," Ackman added.

"I do respect Bill," Icahn added. "What the hell am I fighting so much for?

Bill Ackman hugs Carl Icahn during the 2014 Delivering Alpha conference in New York City.
David A. Grogan | CNBC

The conference had teased its attendees about a mystery guest who would appear on stage with Icahn. The identity was a secret until Ackman came on stage following remarks by Icahn. Facilitating the meeting Wednesday was CNBC's Scott Wapner, who conducted the vitriolic phone interview between the two men last year.

Wapner on Wednesday presented both men with special T-shirts. They said "Bill and Carl reunited" on the front "It feels so good" on the back.

Ackman and Icahn agreed on the importance of activism in improving companies.

"We want the businesses we own to thrive after we exit," Ackman said. "We can speak the truth without fear of losing a 401(k) account."

Icahn briefly weighed in on Herbalife, the stock the two have battled over (Icahn is long and Ackman is short).

"I'm proud of it...we haven't sold one share," Icahn said of his investment. He declined to comment further.

"It's not about winning," Ackman said on Herbalife. "I would love to find a way to get Carl out of this stock."

Read MoreCarl Icahn defends Bill Ackman, slams Marty Lipton

The two men were not always so nice to each other.

"I've really sort of had it with this Ackman guy," Icahn said at one point during their CNBC fight last year.

"Carl, you think I want to invest with you?" Ackman charged later.

"I wouldn't invest with you if you were the last man on Earth!" Icahn bellowed in an exchange typical of the exchange's tenor.

Read MoreIcahn, Ackman in epic showdown of billionaires

The first signs of a detente were in April, when Icahn defended Ackman's bid for Allergan in a CNBC interview.

"We have our differences, but I never said he's not a smart guy. I think the concept of this is good. I hope it works out better for him than Herbalife did, and I think it will," Icahn added shortly after taking sips from a martini passed to him while on camera. "There's nothing wrong with making a bid for a company and using someone else's funds."

The two then spoke on the phone later in the month to make peace, according to The Wall Street Journal.

Read MoreThe feud's over! Ackman, Icahn are friends again

—By CNBC's Lawrence Delevingne

More from Delivering Alpha

Paulson: M&A activity to continue for some time
Druckenmiller: These two investors still have 'guts'
Jane Mendillo, President and Chief Executive Officer, Harvard Management Company
Harvard's endowment CEO: No regrets
Jim Breyer and Shana Fisher (right) talk with Kara Swisher
Google likely trillion dollar company: Tech pro
Omega Advisors CEO Leon G. Cooperman speaks at the CNBC Institutional Investor Delivering Alpha Conference in New York.
Cooperman: Buy Citi, SandRidge and these other stocks now
Ken Griffin
Ken Griffin gives backing to Time Warner-Fox deal