Princess Diana hid Harry's gender from Prince Charles over startling reason

Princess Diana knew she was expecting a boy, during Harry's pregnancy, but did not want Charles to know this as he always wanted a daughter. 

Due to this, Charles was filled with disdain after he got to know he has been blessed with a son, for the second time, upon Harry's birth.

The revelation was made by royal biographer Andrew Morton, who wrote in transcripts of his and Princess Diana's unfiltered conversation in the re-release of Diana: Her True Story - In Her Own Words.

Diana told Morton how she knew the sex of the baby before he was born, but did not tell Charles as he wanted a daughter.

"He wanted two children and he wanted a girl," Diana explained

When Harry was born, she claimed Charles' reaction was, "Oh God, it's a boy," followed by, "and he's even got red hair."

"Prince Charles never really stopped expressing his disappointment at the birth of his second son," a source said.

During Harry's christening, reports suggest Charles told Diana's mother, "We were so disappointed - we thought it would be a girl."