The wedding gift from Queen Mary to her daughter in law – Princess Marina of Greece, Duchess of Kent in 1934 and one of the principal presents was:
Rectangular diamond brooch with a ruby and diamond bow ornament diagonally across it>>
The brooch was not seen later in public, but Queen Mary was a collector of interesting jewels. Sometimes from her family or other heirlooms.
I believe the Duchess of Kent sold the brooch later without the double ruby bow, after the early death of the Duke of Kent, when she needs money, back to the royal family.
It is very similar to the brooch which was worn by Camilla, the Queen Consort at Royal Ascot 2023 and before at Christmas 2022 Sandringham.