Until we have a proper HQ picture of this brooch, it will be impossible to identify, it is a shame in most pictures I have seen, the brooch has been entirely hidden by HRH's hair.
This could simply be a diamond spray brooch with no previous royal connection, in which case it will be impossible to identify.
If it is a piece from the family collection, it could be: - The Queen's Vanguard Rose Brooch (Menkes, p. 138) - The unidentified pearl and diamond spray that features on Plate 1 of Queen Mary's photographic jewel inventory (Roberts, p. 113)
It will be impossible to know more until a clearer picture is found, or information is released by St. James's Palace on HRH's outfit.
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