Basically, there are rumors circling that no royal woman will be allowed to wear a tiara at the coronation — including the UK’s next intended queen, Kate Middleton.
When you directly compare this coronation to Queen Elizabeth II’s, almost every royal woman donned a tiara. And there are two main speculations as to why this may be happening:
1. Remember when we discussed the housing crisis and protests? Well. Having royals walk around in millions of dollars worth of jewels is not a good look right now.
2. This one is a bit more sinister, but when it was expected that Meghan Markle may make an appearance, it was rumored that the palace was planning on how to keep her attendance as neutral as possible. One such suggestion may have been to keep her from wearing a tiara. But that would have been very awkward, and potentially made her stand out more, so the conclusion was that no royal woman wears one.
Source: https://www.buzzfeed.com/alexalisitza/drama-before-king-charles-coronation