For his entire life, Prince Harry has been dogged by one very vicious story. But some say this photograph could finally end it.

We've all heard the nasty speculation about Prince Harry's parentage.

For most of his life, rumours have swirled that the young royal's father was not Prince Charles, but actually Princess Diana's riding instructor James Hewitt.

James Hewitt had an affair with Harry's mother, Princess Diana. Photo / Getty Images
James Hewitt had an affair with Harry's mother, Princess Diana. Photo / Getty Images

The pair did have a five-year affair, and over the years many have claimed Prince Harry bears a strong resemblance to Mr Hewitt — thanks largely to their shared red hair.

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But now, a photo of a young, dashing Prince Philip has gone viral on social media thanks to his "uncanny" likeness to his 34-year-old grandson.

The photo in question was taken in 1957, when Prince Philip was in his mid-30s — roughly the same age Prince Harry is now.

It appeared on the front cover of Paris Match magazine, and shows Queen Elizabeth's husband, now aged 97, wearing a military uniform.

Getty photographer Chris Jackson snapped a photo of the vintage publication and shared it on Instagram this week with the caption: "I spotted this beautiful 1957 vintage cover of a @parismatch_magazine … Who does it remind you of?"

The similarities between Harry and his grandfather at the same age are striking. Photo / Getty Images
The similarities between Harry and his grandfather at the same age are striking. Photo / Getty Images

According to the UK's Evening Standard, the old photograph shows the elder royal "wearing the tropical dress of the Blues and Royals" — the same uniform worn by Harry at the ANZAC memorial in Sydney over the weekend.

Mr Jackson also posted a picture of Prince Harry wearing a similar outfit at his May wedding to Meghan Markle — and the resemblance is striking.

The post has since gone viral, receiving thousands of likes and comments.

"Think this photograph may put some of those ugly rumours to bed," one follower posted, while another wrote: "Let's put the James Hewitt saga to rest!"

Others claimed they mistook Prince Philip for his grandson at first glance.

"That's amazing! The resemblance is spot on. I thought it WAS Harry on the Paris Match cover and had to re-read the post. Awesome comparison," one Instagram user wrote, while another added: "What a find. Uncanny resemblance. Quite handsome both of them."

However, some argued the resemblance might be less incredible if the royal pair weren't dressed in similar clothing with both sporting beards.

Others also took the opportunity to point out other royal resemblances, with one claiming: "I think Princess Charlotte is the spitting image of Queen Elizabeth!"

Mr Jackson is in Australia at the moment, following the Duke and Duchess of Sussex on their royal tour.

James Hewitt, now 60, became a household name in the mid-90s after publicly revealing his affair with Princess Diana, which took place between 1986 and 1991 — while she was still married to Prince Charles.

And in 2003, he made global headlines yet again after trying to sell 64 personal letters from Diana for £10 million ($A18.3 million) — a move widely considered to be an act of betrayal.

Ever since news of the affair first broke, the conspiracy theory that Mr Hewitt was Prince Harry's true father has persisted.

Over the years, many have called for Prince Harry, the sixth in line to the throne, to take a DNA test to prove his lineage.

However, the palace has always remained tight-lipped on the matter, refusing to make any official statements regarding the royal father-to-be's paternity.

Prince Harry's first child, with new wife and former Suits star Meghan Markle, is due early next year.