Prince Harry reveals what he thought of Kate Middleton when he first met her

Prince Harry has revealed what he thought of Kate Middleton when he was first introduced to his brother's then girlfriend, explaining that he liked seeing her laugh and making her giggle.

Prince Harry's book, Spare, was officially released in the UK today and has already topped Amazon's bestseller list with a number of bookshops staying open until midnight last night to meet demand.

While there are a number of explosive revelations in the book, there have also been some touching reflections about his relationships, including his initial thoughts on his sister-in-law, the now Princess of Wales.

"I liked his new girlfriend. She was carefree, sweet, kind. She'd done a gap year in Florence, knew about photography, art. And clothes. She loved clothes," he wrote of the period after Kate and William got together.

Recalling the now infamous party, at which he caused upset and outrage across the globe when he decided to wear a Nazi uniform at a fancy dress party in 2005, Harry described laughing with Kate about his brother's own outfit.

"I forget what native or colonial thing she was wearing to the party, but with her help Willy had chosen for himself some kind of... feline outfit," Harry writes in Spare.

"Skintight leotard with (am I remembering this correctly?) a springy, bouncy tail. He tried it on for us and he looked like a cross between Tigger and Baryshnikov.

"Kate and I had a great time pointing our fingers at him and rolling around on the floor. It was ridiculous, especially in a three-way mirror. But ridiculous, they both said was the point of the upcoming party."

In another extract Prince Harry explains how he "liked seeing Kate laugh" adding, "Better yet, I liked making her laugh. And I was quite good at it. My transparently silly side connected with her heavily disguised silly side."

Watch: Prince Harry's memoir divides public opinion

Harry went on to admit though that he had concerns about William becoming too caught up in his relationship to spend time with him, but he "consoled" himself with thoughts of the laughter him and Kate shared and would continue to share.

"Whenever I worried that Kate was going to be the one to take Willy from me, I consoled myself with thoughts of all our future laughing fits together, and I told myself how great everything would be when I had a serious girlfriends who could laugh along with us. Maybe it would be Chelsy."

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Indeed Harry and Kate have been photographed sharing a joke many times over the years during their joint engagements over the years.

The pair have known one another since their early adult years, with Kate having met Harry's brother William at university, while they were both studying at the University of St Andrews.

As William's girlfriend, Kate often joined her future husband and Prince Harry on family holidays and at official royal engagements and the trio were often pictured sharing a laugh together.

At the Order of the Garter ceremony in Windsor in 2008, Harry made sure that Kate felt at ease at such a public outing by making her laugh and Kate clearly made her future brother-in-law chuckle during the RBS Six Nations Championship match between England and Italy at Twickenham on February 2007 in London.

And who could forget the infamous royal relay race in 2017 when the trio joined 150 volunteers for Heads Together, laughing away as they ran the first part of a five-person relay race at the London Marathon Community Track?

Another joyful event was when the royals visited the Harry Potter film set at Warner Bros. Studios in 2013, giggling as they played with wands during their tour.

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Indeed, as further indication of their close relationship, when William and Kate announced their engagement in 2010, Harry described his happiness about the union.

"I've always wanted a sister and now I've got one. I've known Kate for years, and it's fantastic that she is becoming part of the family," Harry told German newspaper Bild.

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In an interview with Tom Bradbury ahead of the book's release Prince Harry also discussed being a third wheel to Prince William and Kate Middleton before he met Meghan.

"I had put a lot of hope into the idea that it would be William and Kate, and me and whoever. I thought the four of us would, you know, bring me and William closer together, we could go out and do work together, which I did a lot as a third wheel to them, which was fun at times, but also, I guess, kind of awkward at times as well," Harry said.

Interestingly, while he describes the laughter him and Kate shared about William's costume for the party, Harry also appears to allege the couple didn't object to his Nazi uniform, and reportedly "howled" with laughter when they saw it.

The Duke of Sussex recently addressed the incident during the third episode of Harry & Meghan, the six-part docuseries which aired on Netflix last month.

He described it then as “probably one of the biggest mistakes of my life”, adding: “I felt so ashamed afterwards. All I wanted to do was make it right.”