Camilla, Duchess of Cornwall sympathised with Princess Diana as she struggled to cope with Prince Charles' strict routine, a new book has claimed.

Prince Charles and his wife Camilla, Duchess of Cornwall

Prince Charles and his wife Camilla, Duchess of Cornwall

Royal biographer Tina Brown claims that usually "upbeat" Camilla found life within the British Royal Family difficult after she married Charles in 2005.

In an extract published from her book 'The Palace Papers: Inside the House of Windsor - The Truth and Turmoil' in The Daily Telegraph newspaper, Brown wrote: "The ambivalence of her position was becoming untenable. For a while, she had thought there was an upside to not being Charles's wife.

"She had always hated flying, speaking in public, dressing up and getting press attention. She had never had a calendar filled with things she didn't want to do, which essentially defines the royal way of life."

The book makes claims that Camilla struggled to deal with the regimented way that Charles ran his life and his expectation that she should do the same.

Brown writes: "The prince's routine was relentless.

"Punctuality had never been Camilla's strong suit, but Charles expected her to be ready for engagements at his own regimented pace. When she asked where they were going, he would snap: 'Haven't you read the brief?'"

Brown suggests that Camilla began to feel sympathy for the late Diana, the prince's late first wife, who also complained about the time constraints placed on her when she became a member of the royal family after marrying the heir to the British throne - the son of Queen Elizabeth II - in 1981.

She writes: "One of (Camilla's) friends at the time told me that she had even started to feel some empathy with Diana's manifold discontents."

The duchess married Charles in Windsor in 2005 but Brown says a health scare almost scuppered the big day.

She wrote: "The otherwise stalwart Camilla went into meltdown.

"She developed a chronic case of sinusitis and spent the week with girlfriends ministering to her shredded nerves. On the day of the wedding, she had to be coaxed out of bed."