Princess Diana kept a huge secret from Prince Charles before Prince Harry's birth

Prince Charles wanted a daughter.

According to Andrew Morton's "Diana: Her True Story," as excerpted in People, Princess Diana recounted in her diaries that her then-husband was "disappointed" when their second child ended up being a boy. In fact, he wanted a girl so badly that, when she saw on an ultrasound that she was having another son, Diana didn't tell Charles out of fear for how he would react.

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"I knew Harry was going to be a boy because I saw on the scan," she explained. "Charles always wanted a girl. He wanted two children, and he wanted a girl. I knew Harry was a boy, and I didn’t tell him."

When Diana gave birth to Harry at St. Mary's Hospital's Lindo Wing, her husband apparently barely attempted to conceal his alleged disappointment.

"First comment was: 'Oh God, it's a boy," Diana wrote. "Second comment: 'And he's even got red hair.'"

See photos of Diana with Harry and William through the years:

Weeks later, at Harry's christening, Charles was still unable to hide his slight resentment about the fact that Diana hadn't given birth to a daughter. At the service, Diana says that he leaned over to her mother, Frances Kydd, and told her, "We were so disappointed -- we thought it would be a girl!"

His insensitive comment led Frances to blow up at Charles.

"Mummy snapped his head off, saying: 'You should realized how lucky you are to have a child that’s normal,'" Diana recounted. "Ever since that day the shutters have come down, and that’s what he does when he gets somebody answering back at him."

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It was Prince Harry's birth that seemingly proved to be the straw that broke the camel's back on Diana and Charles' marriage, too, as Charles rekindled his affair with his now-wife, Camilla Parker Bowles.

"Suddenly, as Harry was born, it just went bang, our marriage," Diana wrote. "The whole thing went down the drain."

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Order Andrew Morton's "Diana: Her Story Story" here.