Hmm, there are several inaccuracies in the article. Princess Mary received the Brooch as a wedding present in 1893 and, as was her way when she became Queen, had a diamond filigree tiara made using the brooch as a central and replaceable element. We have only seen photos of it with the diamond brooch.
The bandeau Princess Margaret wore was the Diamond and Sapphire Bandeau. I never liked the bandeau from the photos, it looked a heavy and clumsy piece with a honking great big dark sapphire that looks like a +-cyclops eye!
However, having seen how delicate and beautiful the Filigree Tiara is, I may have to eat my words if we ever see Cyclops again.