Watch: Holly Willoughby clashes with Vanessa Feltz on This Morning
Appearing on This Morning, Feltz took aim at Markle for wearing a £990 dress to the One Young World summit in Manchester on 5 September.
Read more: GMB's Ben Shephard defends Meghan Markle
Of the outfit, Feltz said: "There's just a girl in a $4,000 Valentino outfit, she's not just a humble girl from Suits!"
Willoughby then defended the former actor: "I don't like it, it's unfair, I wonder how much Harry's suit was. Do you know what I mean, I bet it's not off the rack either, I'm just saying I think it's unfair to talk about her outfit."
Willougby's This Morning co-host Philip Schofield also defended Markle, saying: "But she will be criticised for anything she does no matter what she does, I have that feeling!"
Feltz was also critical of the content of Markle's speech at the summit.
She said to Willoughby and Schofield: "She doesn't come across all that sincere and I just thought she should have been like 'well enough about me let's talk about you' or equality, diversity, world peace or any of the very important topics we're shining a light on."
Feltz has been a frequent critic of Markle but did defend her when the Duchess said she had been the subject of racist abuse.
The broadcaster said on This Morning last year: "If Meghan feels that she was subject to racism, then it's not for us to disagree - only she knows how she felt.
"I'm a Jewish woman and I would not appreciate it if I said I had been subject to anti-semitism and somebody else tried to tell me I hadn't."
Markle recently launched her podcast Archetypes on Spotify with her first guest being tennis legend Serena Williams.
Watch below: Watch below: Meghan and Harry arrive to cheers at One Young World summit.