Royal wedding 2018: Will Meghan Markle's gown follow the unspoken royal dress code?

What will Meghan wear?

What will Meghan wear?

Once upon a time... royal wedding dresses were richly coloured

Queen Mary I was married in purple in 1554 - reserved exclusively for royals

In 1816 Princess Charlotte wore real silver thread with silver embroidery

Then Queen Victoria chose a simple white dress in English silk and lace

And set the pattern for white weddings ever after

The Queen Mother broke the mould in a loose flapper-era gown

But there are some style rules almost all royal dresses follow

No knees, please - royal dresses are nearly always full length

Since the 50s, skirts have slowly increased in volume

Sweden's Crown Princess Victoria went for an 'off-the-shoulder' look

But sleeves are still the done thing for most royal brides

A couple more finishing touches help define the royal look...

A train adds a sense of grandeur as you glide to the altar

And a veil remains quintessential for a royal wedding - Kate wore one too

The timeless princess role-model remains Grace Kelly in a high neck and full sleeves

Quite different from the layered tulle dress Meghan wore as an actress in Suits

But maybe she has a few surprises for us - we'll soon find out