Princess Diana’s signature hairstyle was a spur-of-the-moment decision.

Sam McKnight, who was the Princess of Wales’ personal stylist from 1990 until her death in 1997 at age 36, opened up about that unforgettable moment.

"The first time I met the Princess of Wales was on a shoot," McKnight told British Vogue on Tuesday. "This leggy blonde comes bouncing up the stairs, smiled and made us all melt, and it was Princess Diana."

McKnight recalled having "a really lovely day" with Diana as they worked on portraits for British Vogue. 

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"I made [her hair] look short under the tiara – I faked it a bit," he said. 

But when the photoshoot wrapped, Diana asked McKnight how he would style her hair if she let him do whatever he wanted.

"I said, 'I would cut it all off and just start again,'" McKnight admitted. "It was the beginning of the ‘90s and it was at the time that I was doing lots of shows and covers and a lot of the girls had short hair, and we were moving from the big frou-frou ‘80s into the sharp, more androgynous, business chic of the ‘90s."

That’s when Diana surprised him.

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Princess Diana had a longer hairstyle before she decided to go for a major chop.

Princess Diana had a longer hairstyle before she decided to go for a major chop. (Photo by Daily Mirror/Mirrorpix/Getty Images)

"She said, 'Well, why don’t you just cut it off now?'" McKnight shared. "So I cut it off then and we never looked back."

McKnight also described how Diana happily met his mother during a visit to a factory near the Scottish village where the matriarch lived.

"My mum and her friends were standing outside and [Diana] had never met my mum before," McKnight explained. "So, I think the story goes, one of my mum’s friends shouted out, ‘This is Sam’s mum,’ and for some reason, the Princess knew exactly who she was talking about and went over and spoke to her and that made my mum’s day. I think for me that was probably the most pride I’ve ever felt in my job."

Most recently, McKnight worked with Emma Corrin, who stars as the late royal in "The Crown." Like Diana, the actress, 25, nabbed her own cover for Vogue.

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The Princess of Wales, circa 1991.

The Princess of Wales, circa 1991. (Photo by Andy Stenning/Mirrorpix/Getty Images)

"From one Princess Diana to another," said McKnight. "I remember that day. That was my first job after the first lockdown in summer [2020] and I remember when the job came in and I wasn’t quite sure that I was the right person to do this."

"And actually it was a pleasure and Emma was a pleasure, and I was quite taken by how alike Emma was to Princess Diana in her looks," McKnight continued. "And she was such a lovely girl that any doubts and fears were laid, and I think it’s a great cover."