ET got the chance to catch up with Cohen shortly after taping the milestone episode, and the host opened up about how the past decade has been a wild ride.
"It does not feel like it's been 10 years," Cohen reflected with a smile. "It feels like it's been the longest and best hangover you can imagine."
Looking back at what he's accomplished over the years, and the success of the show, Cohen said, "I attribute the longevity of the show to the authenticity of the experience."
"We are literally hosting a live party every night at 11," Cohen explained. "You don't know what can happen. Sometimes things can go terribly wrong. Sometimes the casts hate each other, sometimes they drink too much. You don't know what's going to happen. And I think people really like authenticity these days."
"Also, I go there in a way that a lot of people don't," he added. "I think that's enjoyable to watch for some people."
During the episode, Cohen and Teigen played a game called "Rate That Decade of Shade," where they went through and scored some of the shadiest, funniest moments from the show's first 10 years.
According to Cohen, Teigen has been a longtime superfan of the show, so having her on for the anniversary episode just made sense.
"Chrissy tweets into the show, she texts me personally, there is no form of communication in which she does not reach out to both the show, to Bravo, to the housewives, and myself," Cohen shared.
The pair also played a game called "Now & Ten," where John Mayer made a surprise appearance as the host of the trivia contest, which Cohen handily won.
"[This was] an amazing anniversary show," Cohen reflected. "Extreme Bravo fandom in Chrissy Teigen, a big star housewife in Countess Luann, a superstar who has nothing to do with any of it in John Mayer."
"It's the exact right recipe for Watch What Happens Live fun," Cohen added.
Watch What Happens Live airs Sundays through Thursdays at 10 p.m. ET/PT on Bravo.