Kelly attempted to steer the conversation away from the Netflix film onto Fonda's appearance, praising her for being "an example" before asking whether she's "proud to admit" she's gone under the knife.
"You admit that you've had work done, which I think is to your credit, but you look fantastic. But you look fantastic", she said.
Fonda briefly paused before answering.
Fonda, looking bemused, replied: "We really want to talk about that right now?" So Kelly tried to backpedal.
"Well, one of the things people think about when they look at you is how unbelievable you look", Kelly said.
Screen grabs of Fonda's face immediately after being asked the question quickly began circulating on Twitter.
Patel also asked Redford, who previously starred in Barefoot in the Park with Fonda early in their careers, for his take on the moment. I take care of myself.
The film stars Fonda and Robert Redford in a tender neighbours-with-benefits situation that enables them to enjoy easy marital intimacy without necessarily engaging in a sexual relationship.
The awkward exchange between Kelly and Fonda was the second time in Kelly's first week as a daytime host that a celebrity interview has gone south.
"So how come @megynkelly didn't ask @RobertRedfcrd if he had any plastic surgery?? Way to stay composed @janefonda #doublestandard". Monday's show (the only one so far for which final numbers are available) drew 2.93 million viewers, up from 2.61 million the previous week but down from the same day a year ago.
Then Kelly said, "You admit you've had work done, which I think is to your credit".
Messing and other "Will & Grace" co-stars appeared on the debut episode of Kelly's new NBC talk show to promote the reboot of their own show. The actress was being interviewed on Today by Megyn Kelly, who is standing in as the presenter for the week.
Fonda opened up in 2012 about going under the knife and the specific instructions she had for her doctor.
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