It's compulsory to wear hats in church
If you've ever watched a royal wedding before, you will understand how important a guests hat can be. Ladies are expected to wear 'appropriate' attire, covering their shoulders, having hemlines that hit their knees and covering their heads.
Meghan's bouquet must contain myrtle
In a tradition started in the 1800s by Queen Victoria when she wed Prince Albert, myrtle, or the 'herb of love', is always in a royal bridal bouquet. Victoria planted the herb in her garden following the wedding and brides — Queen Elizabeth, Diana and Kate, included — have had it in their bouquet ever since.
Prince Harry will be dressed in his military uniform
Prince Albert was the first royal groom to don his military uniform in 1840 when he wed Queen Victoria. Since then, grooms have done the same and it's likely Harry will follow suit. Both Prince Phillip and Prince Charles wore their naval commander uniform, while Prince William wore his Irish Guard Colonel garb.
Prince Harry spent 10 years in the army, completing two tours of Afghanistan and had the rank of Captain, so expect him to be a man in uniform like the men who came before him.
Meghan will only be allowed to wear neutral nail polish
Bride Meghan unfortunately won't be able to don a special nail for her special day - instead a royal rule for official events remains that nails must be natural-looking.
Guests are not allowed to wear wedges
It's a well-known fact that Her Majesty is not a fan of wedges, and so an unofficial rule for guests attending the royal wedding is they must not wear the heel.