This is why Kate Middleton can wear a tiara, but Meghan Markle can't...

Over the weekend, royal watchers got excited after a photo surfaced of Meghan Markle at her prom in high school.

In the picture, the future royal can be seen in a lilac strapless gown wearing a tiara - as she was crowned homecoming queen.

Fans loved the old photograph saying "now we get to see just how stunning she's going to look".

But if they're expecting to see the 36-year-old wearing a tiara again in the coming months, they'll have to wait a bit longer.

That's because it's royal protocol only married women are allowed to wear tiaras.

As explained by etiquette expert Grant Harold, the tiara signifies that one is off the market and not looking for a husband.

Which means after her royal nuptials to Prince Harry in May of this year, Miss Markle will be allowed to do the same.

So will the former 'Suits' actress follow in Kate Middleton's footsteps and wear a bejeweled headpiece on her wedding day?

Royal expert Ingrid Seward says: "She might have the Spencer tiara, which is also Harry's heritage and is the one Diana wore on her wedding day."

However, according to Harold, tiaras are supposed to be an evening-only accessory - so it's also a possibility the bride-to-be will until after the wedding to make her first appearance in a royal tiara.

"Flashy diamonds and tiaras are not worn during the day," Harold told the BBC.

But it wouldn't be the first time the actress has broken a royal rule or two. So we will just have to wait and see!