Princess Diana reportedly felt her son Prince Harry would one day feel "inadequate" around his brother, Prince William.
The Duke of Sussex's late mother is thought to have aired these feelings when the boys, who now live separate lives, were much younger.
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In his bombshell memoir released last year, Spare, the former working royal spoke of his anger at being called a "spare" by his father King Charles.
"Wonderful! Now you've given me an heir and a spare – my work is done," the monarch is thought to have told his then wife, per the prince.
Now Royal biographer Ingrid Seward has suggested this resentment had a much bigger meaning, and was once raised by Diana.
"[Diana] was very concerned about [Harry's] feeling of inadequacy with William. Even when they were very little," Ingrid told The Sun.
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"When Harry went to Miss Minors, which was the baby school, after William had been there, the teacher there said to him 'here Harry, play with this clay, William used to be really good at making model figures'.
"Harry threw it down and said 'no! ', so from a very young age, Harry felt inadequate. It was nothing to do with Diana, nothing to do with Charles, but it was just there."
In Spare, the Duke of Sussex accused the royals of racism and claimed William described Harry's wife Meghan Markle as "difficult" and "rude".
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