"Clearly editors are there to make their own decisions, but you know that there is a process ongoing in this country which is looking at the media," she said.
A French lawyer who is an expert in media law said the couple would have clear grounds for an invasion of privacy case. Last week, French first lady Valerie Trierweiler won a judgment of €2,000 ($2,580) after the publication of photos of her in a bikini.
"French magistrates take into account the victim's behavior, when the person is flaunting themselves on camera. Kate Middleton will get damages because she's not behaving in this way," said the lawyer, Anne Pigeon-Bormans.
It is common for women in Europe to sunbathe topless, both in private gardens and on public beaches.
Pigeon-Bormans said Diana's relationship with the press was more complicated.
"Diana and Kate are two very different people. Diana had an unhealthy relationship with the press, there was an ambiguity: she would flee them, then court them," she said. "I don't feel that with Kate Middleton, she is more balanced."