New York (CNN Business) Fox News apologized to Swedish climate activist Greta Thunberg Monday night for a guest's comments during a segment earlier that evening.

Conservative pundit Michael Knowles brought up Thunberg, the 16-year-old activist who addressed the United Nations General Assembly Monday, during a conversation on "The Story with Martha MacCallum" about a Bloomberg editorial piece on giving up meat.

"None of that matters because the climate hysteria movement is not about science. If it were about science it would be led by scientists rather than by politicians and a mentally ill Swedish child who is being exploited by her parents and by the international left," Knowles said.

The segment's other guest, progressive pundit Christopher Hahn, interrupted Knowles' remarks and told him, "Shame on you." Fox News anchor Harris Faulkner, who was subbing for MacCallum, let Hahn respond further, "You're a grown man and you're attacking a child. Shame on you."

A clip of the segment spread on Twitter, with Knowles doubling down on his comments in a retweet of the video . "Her mother wrote a book about her mental issues. There is nothing shameful about living with mental disorders. What is shameful is exploiting a child—particularly a child with mental disorders—to advance your political agenda," he tweeted.

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