Prince Harry kisses Meghan Markle on the cheek at the Invictus Games closing ceremony Getty

Prince Harry has taken a slightly different approach to royal life than his elder brother William, often regarded as the 'Playboy prince' who made headlines for wearing a Nazi costume and being filmed playing 'strip billiards' in Las Vegas.

He's also gone down a very different road in terms of relationships and has been romantically linked to a string of high profile women including Jenna Coleman, Caroline Flack and Mollie King among his more long-term girlfriends such as Cressida Bonas and Chelsy Davy.

Prince William, 35, has only ever gone public with his now-wife, Kate Middleton, who he started dating in 2003 after meeting in university and has been married to since 2011.

While well-behaved Kate has a clean history and the couple seldom hold hands or kiss in public, Harry, 33, is changing British royal history with his very modern romance with 36-year-old US television actress and divorcee Meghan Markle, who prides herself on "being a strong, confident, mixed-race woman" and humanitarian.

Harry and Markle are in the throes of new love, and were pictured holding hands and cuddling up at the Invictus Games earlier this month. The fifth-in-line to the throne even boldly kissed his girlfriend on the cheek at the closing ceremony in Toronto.

While the couple were not on an official engagement, they were dressed casually and appeared relaxed in each other's company. Royal commentator Richard Fitzwilliams points out that we wouldn't see William and Kate act as such if found in the same position.

He told IBTimesUK: "It's a totally different situation. Prince Harry has an unconventional image anyway, his appearance holding hands with Meghan and their kiss delighted journalists who were expecting to see them together at Invictus but not as intimately. He wasn't carrying out formal duties at the Games at the time.

"You would not expect William and Kate, our future King and Queen Consort, to engage in public displays of affection.

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The Duke and Duchess of Cambridge visit The Sunken Garden at Kensington Palace on 30 August 2017 Chris Jackson/Getty Images

"Their chemistry is obvious without the need to show it. Kissing or holding hands in public would be out of place in official engagements. If they did the body language and not the function they are attending, it becomes the story, and it is a worldwide one given the enormous interest in the royals," he continued.

Body language expert Judi James doesn't agree that William and Kate are abiding by royal protocol, and their lack of public affection is more to do with the duke's "personal phobia about PDAs [Public Displays of Affection] with his wife".

She said: "I really don't buy into the theory that William and Kate's hands-off approach is anything to do with royal protocol and that they are somehow under restrictions that don't apply to the gloriously tactile Meghan and Harry.

"For a start, the Queen herself has always been perfectly happy to hold Philip's arm in public and even to discreetly hold hands when the mood takes her – although this gesture is more about Philip offering a helping hand in more recent years – and Charles and Diana were as tactile as any other newlyweds back in the day, holdings hands, kissing on the lips and even placing hands on thighs and even Diana's bum in public.

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19 November 2007: The Queen and the Duke of Edinburgh walk at Broadlands in Romsey, southern England, as they prepare to celebrate their diamond wedding anniversary Fiona Hanson/Pool

"William and Harry have never been immersed in protocol, and the idea William has been barred from doing anything other than the rather odd and formal 'fig leaf' hand poses he and Kate chose to perform in public is probably ridiculous.

"Any hands-off protocol that does exist is more likely to be William's own creation and I believe there is one very good why he has a personal phobia about PDAs with his wife."

James believes that William's coyness may stem from the frenzied media attention that was on his parents' marriage and divorce, adding: "William's huge concern when he selected his new bride was that she would fall victim of the same levels of frenzied public attention and interest as his mother.

"From the moment Diana and Charles went public with their relationship the press camped outside her home and intruded into her every waking moment and of course there are still theories that suggests that the constant form of hounding somehow contributed to her death."

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A young Diana relaxes with Prince Charles in a loose pink dress and matching hat with bow detail during their first official Australian tour together in 1983. Getty

She notes that Kate and William's less touchy-feely public relationship is a smart move.

James continued: "Kate's body language and her style are flawless but they lack all those dramas that leave us slobbering for more. We can see she and William are happy but the pair tend to throw a veil over any displays of moodiness, rows or even strong affection or sexual attraction. This has been a very smart move and - sadly - a lesson that Harry will probably learn the hard way with Meghan.

"Harry and Meghan probably gave us more PDAs in their Invictus outing than William and Kate have during their entire marriage and already you can feel the interest revving up.

"Harry is far more casual and spontaneous than his rather anxious and shy-looking older brother and with no claim on the throne he probably thought that - like his cousin Zara - he can lose the filter and behave like any other young man in love in public," she added.