Within 24 hours of the announcement that she had been signed up by Weight Watchers in the US - for a reported fee of a million dollars - she said she had used some of its ideas on her "chunky" elder daughter. After seeing her in a swimsuit, she told her to cut out bread, chips and fizzy drinks, she said.
Yesterday the United Kingdom arm of the company made clear its disapproval. Linda Huett, vice president of the UK firm, said: "Weight Watchers UK does not believe that children should ever be encouraged to diet."
Children under 10 were barred from its slimming clubs and those between 10 and 16 needed written permission from their family doctor as well as parental consent, she said.
Talk of a diet for Princess Beatrice came a day after the Duchess spoke of feelings of "hopelessness" about her weight problems as she was named the new public face of Weight Watchers. The deal involves the Duchess promoting the benefits of achieving a "healthy weight" to the US public. She will not be doing so for the separate, UK Weight Watchers organisation.
A spokesman for the Duchess said her comments were taken out of context and reflected "normal" advice given by mothers to children about eating.
At a news conference in New York, the Duchess said the contract required her to "keep and maintain a healthy diet so I can keep fighting fit". She admitted being wounded by being dubbed "the Duchess of Pork". She would not confirm reports she would receive a million dollars a year (pounds 660,000) under the deal. In the later interview in New York, the Duchess said: "I very much fear Beatrice is blessed with her mum's genes.
"I mean, she is only eight, but she definitely can pack it on a bit."
Recalling a recent holiday, the Duchess went on: "When she put on her swimsuit, we noticed she was kind of appearing a bit chunky.
"So I began explaining a little of the Weight Watchers' regime. I said: `OK, that's it. From now on, today only, no bread. And no more fizzy drinks.'"
She added: "Poor Baby. I think over-eating sort of runs in the family."
Ms Huett said Weight Watchers UK had "very strict procedures" about slimming advice for children. These included insisting that the youngster's own GP set the "goal weight" at the outset. Young people also had to be accompanied by a parent or guardian when attending sessions.
The spokesman for the Duchess said: "She was really suggesting that healthy eating was important, and was in no way suggesting a diet. This was a normal conversation between a mother and daughter which has been blown way out of proportion."