According to royal biographer Andrew Morton, Kate gave up her 'independence' when she got back with the future King following a short split in 2007.
In his 2011 book William and Catherine, Mr Morton wrote: "There was, however, one casualty of this romantic reunion: Kate herself."
Mr Morton claims that some of Kate's friends thought she was "giving up independence for conformity and adventure for safety."
He went as far as to suggest that the couple's split was welcomed by some of Kate's closest confidants.
His claims came after it was revealed Kate had been training hard and planned to participate in a boat race with her close pals during the time of her split from Wills, however she pulled out at the last minute.
"Please don't drop out. For the first time in your life you are actually doing something for yourself," race organiser and friend Emma Sayle told Mr Morton of what she had said to the Duchess.
"It was as if the last three months of relative independence had become another country."
In the same book, Mr Morton also revealed how Kate struggled during the early days of her romance with William.
"Obstinate and strong-willed, William could be an overwhelming presence and, at times, Kate felt taken for granted - treated like a servant rather than his girlfriend," he explained.
A close university friend of the pair apparently told Mr Morton: "He (William) could flip and curt her. She didn't like it when he ignored her and got into conversation with someone as though she wasn't there.
The pal continued: "He expected Kate to run after him and the longer they knew each other the more he seemed to keep her on a tight leash."
WATCH: Prince William and Kate Middleton attend Buckingham Palace Garden Party