Princess Diana 'Used to Get Very Upset' Over Rumors About King Charles Not Being Prince Harry's Biological Father

Prince Harry 's hair color fueled rumors about his paternity , but an insider revealed just how painful the speculation was for Princess Diana .

According to the late royal's former hairdresser Richard Dalton , "it’s not possible" for Diana's old flame James Hewitt to be the Duke of Sussex's dad.

"It was tough," Dalton admitted to an outlet. "Harry was already born a while before her relationship with Hewitt. And I don’t think it’s possible."

"But no," he stressed. "Harry and the Spencer family have red hair. Charles , Diana’s brother, had bright red hair when he was [in] college. And I used to cut his hair then. [Diana’s sister] Sarah , has bright red hair. [Diana’s other sister] Jane was more or less the same coloring as Diana."

The fashion icon "used to get very upset" about people believing her youngest child wasn't a Windsor .

"The red hair was a trait from the Spencer family," Dalton wrote in his new book, It’s All About the Hair .

Diana and Hewitt's romance spanned from 1986 to 1991, but Harry was born two years before the pair met in 1984.

"I knew nothing about their affair and was not involved with any of the rendezvous, other than maybe unwittingly doing Diana’s hair each day," Dalton penned. "She was certainly giddy at times when she talked about him because it was all new to her; however, we need to remember the context in which this all took place."

Throughout Diana's marriage to King Charles — the then-Prince of Wales — was involved in an affair with his now-wife, Queen Camilla . The love triangle plagued Charles and Diana's union and became the focal point for Netflix's royal series The Crown.

"Diana was starved of affection and intimacy from her husband, the man she loved," Dalton explained. "She was also an heir-making machine for Charles and was coming to terms with the betrayal within her marriage."

"It saddened me to see James Hewitt, by virtue of his tell-all book, clearly signal that this relationship was a conquest and not a matter of love at all. He got her at her most vulnerable and, for her, he was just the first man who rolled along – a twist of fate, time and place. If it had not been him, it would have been someone else."

In Harry's lawsuit against the Mirror Group, he cited the "Plot to Rob the DNA of Harry" article as evidence of unlawful journalistic practices .

"Numerous newspapers had reported a rumor that my biological father was James Hewitt, a man my mother had a relationship with after I was born," Harry told the High Court. "At the time of this article and others similar to it, I wasn't actually aware that my mother hadn't met Major Hewitt until after I was born."

Never miss a story — sign up for the OK! newsletter to stay up-to-date on the best of what OK! has to offer. It’s gossip too good to wait for!

The various columns were published after Diana passed and left the veteran questioning his reality.

"At the time, when I was 18 years old and had lost my mother just six years earlier, stories such as this felt very damaging and very real to me," Harry admitted. "They were hurtful, mean and cruel. I was always left questioning the motives behind the stories. Were the newspapers keen to put doubt into the minds of the public, so I might be ousted from the royal family?"

Dalton spoke to Fox News Digital .