Simmons, who has 28 years of experience working for WNBC-TV, let the expletive fly after she seemed to get angry while shooting a promotion Monday night, the New York Post reported Tuesday.

"What the f - - - are you doing?" Simmons yelled out while she was off camera but still on the air.

"I'm truly sorry. It was a mistake on my part, and I sincerely apologize," she said in an on-air apology about 30 minutes after the slip-up.

A WNBC spokeswoman said she could not explain what prompted Simmons to yell out the swear word.