To anyone unfamiliar with radio host Mike Francesa, the mass of people chanting “Numbah One” and “Hello Dear” while wearing Diet Coke shirts Saturday must have seemed bizarre.

For devotees of the WFAN sports personality and members of his cult following on the Internet, though, this was just the third annual FrancesaCon.

Francesa was in attendance for the second straight year at Manhattan’s Irving Plaza and delivered on a promise he made at the last event, bringing former co-host Chris Russo with him.

“This kind of outpouring is just unbelievable,” Francesa said of the fan convention held in his honor. “It’s so much different than anything else. It’s so spontaneous . . . It’s just wild, it really is. I went through it last year and [Russo] saw it this year for the first time.”

“They love the show. That’s the bottom line,” Russo said of “Mike and the Mad Dog,’’ which they co-hosted from 1989-2008. “Mike and I [did] that show for 19 years. [It] means a lot to a lot of people, so when you come to this event, you see that. It makes you feel good.”

Rockville Centre’s Michael Leboff and New Jersey’s Ron Haraka first organized the event two years ago at a bar in New York City before moving to Irving Plaza last year to accommodate a larger audience. Proceeds from the event went to the Dr. Theodore Atlas Foundation, which focuses on helping children in need.

“The hype levels are higher than they’ve ever been,” Haraka said. “When we first started it, we had no idea it was going to be this big. We thought it would just be us, our friends and family, and maybe a few guys who really wanted to make the effort to come out.”

“It’s been great to watch [this] organically grow from nothing,” said Leboff, who said he and Haraka joked about reuniting Francesa and Russo after the first FrancesaCon. “Now it’s actually happening and the first time they’re appearing in front of a crowd together [again] is here.”

Many fans came in shirts bearing Francesa’s face or inside jokes featuring Francesa quotes and catchphrases. For the third time, Max Lucci of Staten Island took things a step further, dressing up in a Diet Coke suit, wearing a pontiff hat made of a Diet Coke box and holding a staff made of empty Diet Coke bottles, a nod to Francesa’s beverage of choice on the air.

“It’s something I look forward to every year,” Lucci said. “[Francesa’s] little quips . . . that maybe you and one other friend might get, everyone here understands them. It’s like an underground club that you connect with.”

Rockville Centre band “Jerry & the Newcomers” performed before Francesa and Russo appeared, and impersonators Bill Buchanan and Mike Benevento also reprised their roles as Francesa and Russo from their popular YouTube videos.

“It’s real humbling to be a linchpin in all of this and bring all these people together that love Mike and love the Dog,” Leboff said. “It’s like a family reunion.”

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