The UFC superstar appeared on Fox News' "Hannity" to announce a $1 million donation to Tunnel to Towers -- a charity created following the 9/11 tragedy to help families of emergency responders who died in the line of duty -- when he got a little too excited.

Speaking with the org's CEO, Frank Siller -- the brother of 9/11 hero Stephen Siller, who lost his life trying to save others in the World Trade Center attack -- McGregor couldn't help but utter a cuss word.

"Frank, I'm honored to support you," he said just seconds after he was introduced by Hannity on the show. "I wanted to say, your brother Stephen is a f***ing -- excuse me, is a hero."

"He's a hero. You're a hero."

Despite the PG-13 language, the audience loved it -- as did Frank, who told Conor, "You had it right the first time!"

Conor then presented the giant check to Frank, who vowed to use some of the money to pay off the mortgage for a family that recently lost a loved one who died while fighting the recent deadly fire in Buffalo.

McGregor later said he was sorry for swearing, telling Hannity, "I would have to curse on Fox. I apologize. I apologize."

But, Hannity told him, "Don't worry about it. It's the one place you can!"