Im not sure this is the wedding tiara either. The one that resembles it most is a small diamond floral tiara auctioned at Sotherby's on july 19th so cutting it close for this wedding. It might have been a present on the morning of her wedding though.
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if you google lady Tatiana Mountbatten tiara - you will see a photo of her on pinterest and there you can see that it is not the Strathmore rose tiara