The Duchess of Cambridge was defended by a charity boss after a scathing attack by novelist Hilary Mantel.
Nick Barton, who heads Action on Addiction, which Catherine supports as patron, described her as an "intelligent" woman genuinely interested in the work of his organisation.
During a lecture at the British Museum, Mantel, who has won the Booker Prize twice, said Catherine appeared to have been "gloss-varnished" with a perfect plastic smile, in contrast to Princess Diana, who she described as awkward and emotionally incontinent.
She said "painfully thin" Catherine was selected for her role of princess because she was irreproachable: as painfully thin as anyone could wish, without quirks, without oddities, without the risk of the emergence of character.
"She appears precision-made, machine-made, so different from Diana whose human awkwardness and emotional incontinence showed in her every gesture."
Mantel, whose latest novels are set in the Tudor court, said she saw Catherine becoming a "jointed doll on which certain rags are hung".
She added: "In those days (Catherine) was a shop-window mannequin, with no personality of her own, entirely defined by what she wore.
"These days she is a mother-to-be, and draped in another set of threadbare attributions. Once she gets over being sick, the press will find that she is radiant.
"They will find that this young woman's life until now was nothing, her only point and purpose being to give birth."
She also blasted Catherine's first official portrait by Paul Emsley, unveiled in January, labelling her eyes as "dead" and wearing "the strained smile of a woman who really wants to tell the painter to bugger off".
The Duchess was due to tour the addiction charity's Hope House treatment centre in Clapham, south London, on Tuesday - her first solo engagement since she presented the BBC Sports Personality of the Year award.
Asked for his reaction to Mantel's criticisms, Mr Barton said: "I don't think it's for me to comment on that kind of stuff. I speak of what I know - somebody who wants to help, is helpful and genuinely interested and is intelligent.
"I've met her several times and I found her to be engaging, I found her very natural, I found her actually genuinely interested in the subject.
"You can tell a lot from people's questions and she asks really good questions. They're not routine stuff, they're questions of someone who wants to learn. I find her very easy to deal with."