The author appeared on ITV's breakfast news show on Thursday to talk about his book Revenge: Meghan, Harry and the war between the Windsors, which has hit headlines with its claims about the Duchess of Sussex.
Journalist Bower has included anecdotes in his book where interviewees have alleged they experienced bullying behaviour or rudeness from Markle.
She and Prince Harry have strenuously denied any accusations of bullying towards staff.
'She thought the monarchy was like Hollywood, all about celebrity. In fact it's about hard work with little reward, and she didn't like that.'
Tom Bower says the rift between the Sussexes & the Royal's has 'both sides to blame but on the whole the blame lies more with Meghan'. pic.twitter.com/fNG09rGrAV
— Good Morning Britain (@GMB) July 21, 2022
In Thursday's interview, Shephard and Bower clashed over whether the former Suits actor was famous in her own right before marrying into the Royal Family.
Shephard said: "I mean Meghan was an independently, successful Hollywood actress, famous in her own right, and ambitious like lots of people are and had a strong view about how she wants to be seen.
"No-one can sort of suggest that isn't the right way of going... sort of what she wants to do, it's her life. Why should she suddenly be judged in terms of what some people say is bullying, and others are saying is just having forthright views?
"I mean she's just trying to control her brand, she's not the first well known person to do that is she?"
But Bower replied: "Not at all, but I think you say, 'she was a famous actress' - she wasn't, she was a third rate..."
Shephard interrupted: "No, that's not true."
Bower argued that he thought Suits had only been watched by a million people, but Shephard again replied: "No, that's not true. She was a very famous actress and she had a high profile in Hollywood and Suits was a series that was streamed all over the world, so people knew who she was."
The author replied: "Well, I won't argue but I disagree with you. But the point is, until she met Harry, even Graydon Carter who works at Vanity Fair and had commissioned the article, had never heard of her and had never heard of Suits, he was just told that whoever married Harry was going to be famous, as she indeed was."
Shephard's stance on defending Markle was very different to his former colleague Piers Morgan's, who stormed out of the Good Morning Britain studio in March 2021 over a row about her and eventually quit the show.
He had called into question Markle's comments about her mental health and racist remarks about baby Archie from a member of the Royal Family which she revealed during her Oprah Winfrey interview.
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