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Oh, what could have been!

During an appearance on "Watch What Happens Live," Anderson Cooper revealed that he and Andy Cohen were once set up on a blind date several years ago, but that face-to-face meeting never happened because Andy broke Anderson's "cardinal rule."

What was this faux pas? Andy got a little too excited about Anderson's famous socialite mother, Gloria Vanderbilt.

"When Andy and I were first set up on a blind date, which never happened because we had a phone call and after two minutes I said, 'I'm not dating this guy,'" he said. "He broke my cardinal rule … he mentioned my mom within the first four sentences of meeting me."

The CNN host said, "If somebody does that, it's a deal breaker."

The Bravo host said that "being a Vanderbilt" means "everything to us." He recalled telling Anderson, "You're mom is Gloria Vanderbilt."

Anderson response: "My thought was, 'And, I'm never dating this guy."

The two are certainly pals now, but nothing more than that. But, they do have great chemistry and they know it. Last year, they even went on tour together for a show they created called, "AC2: An Intimate Evening With Anderson Cooper & Andy Cohen—Deep Talk and Shallow Tales."

"He and I have good chemistry. It just works," Andy said at the time. "We're really good friends, so we're taking the show on the road."

Over the years, many have tried to link them together, but both are now in committed relationships with other men. Even Andy admits that things probably worked out for the best, so perhaps his Gloria Vanderbilt fascination was actually meant to be.

"We were set up on a date. Not many people now this, but the way Anderson I met about 20 years ago is we were set up on a blind date," he told E! News last year. "It didn't take. It just didn't work. We're meant to be good friends and not boyfriends."